Reading through the numerous posts and comments on corporations as people, particularly with respect to free speech and the Citizens United case, I've been frustrated with the lack of clarity and thoughtfulness on this issue. Here is my attempt to explain my thinking on these issues. This is going to be long; there is no TL;DR substitute.
Here are some common arguments I see being made in support of Citizens United: "Corporations are just groups of people, so restricting their speech is restricting people's free speech". "This isn't about corporate personhood, it's about free speech!" On the other side, often the arguments revolve entirely about how corporations aren't people, which is technically correct but isn't really getting at the issue.
To start with the blatantly obvious: Corporations are not people. Period. This shouldn't even need debating. Anyone who has progressed beyond Abstractions 101 should agree with this.
What are corporations? They are groups of people endowed with certain legal characteristics to facilitate economic activity. This is the most important part: "economic activity".
According to Wikipedia, common characteristics of corporations include "Legal personality, Limited liability,Transferable shares (ownership), Centralized management under a board structure". One should recognize that many of the economic rights of an individual are also available to corporations (such as legal personality, property ownership, the ability to enter into contracts, etc.) because we want to facilitate the ability of corporations (groups of people) to participate in economic activity. This is what corporate personhood means: not that they pump blood through veins, but that we give them rights that are originally thought of as individual rights to facilitate group activity.
But, and this is probably the most important sentence: Corporations should not have the political rights of the Individual simply because they have the economic rights of the Individual.
Society and government CAN and SHOULD give different groups of people, made for different purposes, different sets of individual rights tailored for said purposes. A group of people should not have ALL the rights of individuals - it depends on the PURPOSE of the group.
This should be pretty obvious if one considers some other "types" of groups of people. Consider religions. A religious group is just a group of people. Does that mean they should have all the political rights of people? Should they be able to endorse and campaign for a specific candidate's election? Spend unlimited money on elections? Tell all their members how to vote? F__K NO. I don't want the Catholic Church or any other religious organization exerting political influence, thank you very much. We have something here in the US called "Separation of Church and State." Should they be able to engage in economic activity, like a corporation? Of course they should be able to sell products (i.e. Bibles) and have finances, but should we give them limited liability? Let a church leader take tons of money from their followers as "loans" and not have to pay it back by declaring bankruptcy? I say no. How about shareholders? Should people be able to buy stock in a church, which then is legally responsible for increasing shareholder value by converting other people and raking in money? Probably not. The reverse holds true too. Government is just a group of people, but we don't want government to have the same rights in the religious domain as a church (restrict membership to believers, for example). Again, separation of church and state.
Other examples might not be so clear and present to American politics today, but are important nonetheless. A military is also a group of people. A country might have a privatized military that is not part of the government. Should a military be allowed the political rights of an individual? To spend unlimited amounts and endorse specific candidates? That couldn't possibly lead to problems, right? How about to engage in economic activity? An organization that has the power of deadly force combined with a profit motive, no problem there, right?
Back to the original point: We CAN and SHOULD regulate different groups of people differently. This is no different for corporations. They are created as ECONOMIC entities, so we give them economic rights, not political ones. Just as there are problems in the previous examples, there are major problems with giving corporations political rights. I'm sure people can think of even more, but here is a sampling:
1. Corporate decision-making is inherently centralized, without much recourse. This is great for economic activity, but is counter to democratic principles. This is pretty important to understanding the human motivations behind this issue, especially the political ramifications. Who makes the decisions? All this talk about corporations just being a "group of people" ignores the reality of the situation. While it is true that it is a group of people, the real nature of the corporation is that it is a large group of people who all work provide a lot of profit to far fewer people, and it is the few at the top who make the decisions and control the spending. This is the reason "corporations" (i.e. the people at the top) like Citizens United - because those at the top would control the political money and power provided by the rest of the "group of people" who have little say. When we say "corporate free speech", what that really means is "amplified speech of those who control corporations". In other words, this is a classic case of undemocratic centralized power. Again, great for operating in the economic domain, but fundamentally counter to democracy.
2. Corporate treasuries are the result of people buying a product or service. People do not and cannot spend money on basic products thinking about the political ramifications. Money that people spend is a vote of confidence in a product and a way of encouraging further development of said product, not to support the political leanings of its executives! In other words, this money is not political. Corporate assets are like a social mandate to continue the economic activities that earned them the profit. Using these assets for political purposes is a gross distortion of the reward system of capitalism. Related is the fact that a person cannot possibly consider the political activities of the corporations when buying products. And some things cannot be avoided. What if you don't like the politics of your local utility? Do you have to give up electricity, hot water, gas, or move? What if you disagree with your local internet provider? No more internet? Or the only grocery store in a rural community? Give up food? We segregate economic and political activity in order to keep these domains separate. Furthermore, why should economic differences lead to democratic differences? Why should a company that operates in a sector with inherently higher margins or sales versus a commodity industry inherently get more political power?
3. The sheer scale of corporate treasuries dwarfs electoral spending. Again, this is because they operate in the economic domain, not the political one. Example: Exxon Mobil made revenues of $383 billion dollars and $30 billion in profits in a single year. The total spent on all federal elections in 2008: $5.85 billion. In other words, a single corporation could spend 20% of its profits or 1.5% of its revenues in a SINGLE year and spend more than all federal candidates - House, Senate, President - combined. And that only happens every 4 years. Again, that's a single corporation in a single year dwarfing all federal elections. Anyone want to compare total corporate profits on a four-year basis? Do we really want to be mixing these two realms (economic and political)?
4. Sovereignty. A corporation has no national allegiance. No citizenship. It almost makes no more sense to say any company is an "American company". At most, one can be based in a country, but corporations nowadays are multinational by nature. They make money all over the world, enter into contracts all over the world, have shareholders all over the world. They have no vested interest in any particular country, the United States included, unless it happens to benefit them financially. That is "ok" (a whole 'nother debate) in the economic realm, but there is no reason to give such entities political power that is reserved for citizens! Along these lines, opening political power up to corporations allow hostile states to interfere with domestic politics. There is now nothing stopping China from funneling money and influencing American politics. The next time a candidate runs with a platform of improving democracy and human rights in China, there is nothing stopping the Chinese government from either creating a corporation or using an existing sympathetic one to funnel money toward opposing him/her. Which side has the deeper pockets?
5. Transparency: corporate dollars are not transparent. Not even close, compared to political organizations like campaigns or PACs. These groups are required to disclose every single dollar of revenue and its source, and every single dollar spent. Corporate money flows cannot be tracked. This allows for foreign governments to exert domestic political power, as in point 4, or simply allows the rich and powerful to greatly amplify their political power. That runs counter to all the historical progress we've made in democracy, which can be understood as precisely reducing centralized power in the hands of the few in favor of equal political power for everyone. We simply can't (and don't want to) impose the sort of transparency that would be required because, say it with me again, corporations are economic entities. Tracking every dollar spent and earned through meticulous FEC-like disclosures would greatly impede economic activity. If you really really want corporate free speech, go ahead and ask them to go along with such disclosure requirements. Good luck.
Back to the core point. Corporations are for economic activity, not political activity. So what about all the complaints that restricting corporate speech inherently restricts speech of people? Bullcrap. Nobody in their right mind would form a corporation to engage in democracy as a group. "Hey guys, if we want to get our message out, we gotta go out and SELL THOSE MICROWAVES!" "Thank goodness we have limited liability to help us reach people!"
The fact is, there are already clearly defined outlets for groups of people to organize for political purposes. A key example is the Political Action Committee (PAC). A PAC can spend unlimited amounts of money as speech for political purposes. There ya go. Of course, it also has restrictions which make it appropriate for the sensitive domain of politics, such as transparency of every single dollar spent. Donation limits ($2.5k per person) seek to limit outsized influence by the few, while still allowing everyone to contribute as much as a typical person would desire. Note the philosophy of this rule: PACs derive their power from the equalized contribution of individuals (i.e. democracy) for the express purpose of political speech; therefore, they may spend unlimited amounts. Corporations derive their power from economic activity; therefore, they should not be allowed to influence the orthogonal domain of democracy. The specifics of what the contribution limit is are not important and can and may be adjusted. The point is that groups of people organized for political purposes have a way of doing so, and corporations are not it. Conflating restrictions on corporate speech with restrictions on group speech is a red herring designed to engender sympathy ("oh noes! not my free speech!") while sidestepping all the problems with corporate speech.
This was also a key issue in the Citizens United case. CU was a non-profit corporation that also ran a very wealthy PAC with millions in assets. They could have spent unlimited amounts from that PAC for the very purpose in that case (distributing their Hillary movie) and abide by all the regulations on PACs . They chose not to and instead spent money from their corporate treasuries. This is not about censorship - there is nothing specifically relevant to the Hillary movie. It is about the source of money: whether that derives from individual democratic power or economic assets.
To summarize, as a society we need to recognize that there are fundamentally different issues at play in different domains of human activity - whether they be democratic, economic, religious, etc. Regulating these appropriately for their domain and enforcing a separation of concerns is critically important for keeping each of those healthy. This is exactly what is at play with respect to restrictions on corporate speech.
This issue is simply another instance of one of the oldest and most important stories throughout history - that of equality and democracy fighting against centralized power that seeks to entrench itself further. Corporations are one of (if not the most) powerful modern vehicles for centralizing power, and while that sometimes makes sense for economic activity, we simply cannot allow that power to bleed unchecked into democracy and politics. I'll end with a famous quote that says it better than I could:
"I hope we shall crush in its birth the aristocracy of our moneyed corporations, which dare already to challenge our government to a trial of strength and bid defiance to the laws of our country." -- Thomas Jefferson