First of all, no one can claim to speak for all Liberals. Liberals' beliefs are not bound by party. Liberals follow no Great Leader, because Liberals think for themselves. Thinking for yourself is part of what makes you a Liberal.
The way Liberals express their beliefs can be fought over endlessly. Their attitude toward any single issue can run the full range. But here is one example of what the core tenets of Liberalism are; there may just be a chance that most Liberals can agree on these.
I should also say that the way the terms liberal and conservative are thrown around in the media and bloggosphere is distorted and misleading. They are used as shorthand for things that nobody actually believes, but it's easier to do that than to deal with actual ideas . . . .
1. Rights: A crucial assumption of the founding documents can be stated this way: The rights of the individual are more important than the power and privileges of government or corporations. Government exists to protect and serve its citizens; not the other way around. Business exists to serve people's needs; not the other way around. Thus, all rights do not have to be spelled out; what has to be spelled out is the ability of government to intrude upon individuals and violate their rights. One would think that this is a basic belief of conservatives, were one to pay attention to only what they say, and not what they do. Conservatives seem to say that if a right isn't explicitly spelled out in the constitution, it doesn't exist. They believe that because rights are narrowly granted in law, they don't apply to foreigners and other categories of "The Other." To Liberals, we're all in this together, and rights, as it says in the Declaration of Independence, have existence independently of explicit laws. And, as it says in the Ninth Amendment to the Constitution, not all rights have been included in the list that the Founders made; they couldn't think of everything. Liberals are thus to be seen as the true holders of the legacy of the Founders. The Constitution is not some final, holy truth; it is a living document. When Conservatives succeed in locking the Constitution in place, it dies. When the Constitution dies, so does America.
My first injected comment: There is an odd subtext to the political theory of the conservatives, which is that political texts should be treated like religious texts. Certain documents should be treated as perfect, divine revelation. They say everything that should or can be said on the topic; they are not subject to change, interpretation, correction, learning, or development. (This is kind of like the idea that no politician can ever admit having made a mistake and learned from it.)
Thus, the Constitution - never mind what it actually says - should be treated as holy writ, and the product of a process of negotiation and compromise between wealthy, land-owning oligarchs becomes the one, single, perfect answer to all problems. The fact that circumstances have changed in the last two hundred thirty years is not important. The fact that we now know more - about the world, human nature, economics and trade, even sociology - than they did then, and have different interests, goals, and capabilities, can be ignored. The Constitution and the Declaration of Independence are great documents. They and the men who wrote them should be studied and revered. But they are not perfect, they are not final, they are not the only answer. We should always pay attention to them. We should then give ourselves the respect we could earn by having the right and ability to learn, change, adapt, evolve, and overcome our problems ourselves.
2. Free Enterprise: Economic freedom is as important as political freedom. Competition is a key factor in economic growth and prosperity. Liberals are not communists. But. Having the government step completely away from regulating the economy threatens economic freedom and free competition just as much as does having the government run the economy exclusively. If the government does not protect individuals and small businesses from unfair business practices, and does not protect the consumer and the employee, then unfettered big businesses will destroy our economy and society. Government is not the only threat to competition; it is often the only way to make sure competition exists.
There are other key factors needed for prosperity than competition; one of them is trust. This is why the Rule of Law is important. There must be consequences for unfair business practices, cheating, lying to customers and investors, and producing products that don't work or do harm. Remember: It isn't and shouldn't be illegal to be a monopoly; it is to act like one.
Some regulations are stupid. They should then be changed or scrapped. That does not mean that all regulations should be done away with. Some rules in sports are stupid; does that mean that all sports should do away with all rules?
This is a good place to talk about Social Security. The Social Security program is an example of common contributions benefiting the common welfare. Because of Social Security, not only senior citizens, but also everyone in America, is better off. Were Social Security to be abolished, as George Bush and many of his supporters want to do, the general level of prosperity in America would fall. Even those who pay into Social Security more than they get out of it would in the long run suffer. Of course, since Bush's supporters would not immediately suffer as much as others, and would continue to enjoy their wealth and status, he and his do not care. Liberals care, and so should those who have been voting against their own interest.
3. Tolerance: No one person has all the answers. No one belief system provides all the solutions to our problems. Thus, tolerance for the expression of all opinions is essential to our survival and the health of our society. The only thing that cannot be tolerated is intolerance.
This is the place to talk about the issues of religion and morality. First and foremost is the idea history has taught us, that any government run according to religious tenets is repressive, and will both hurt its people and (we hope) fail. That is why the separation of church and state was the first principle mentioned in the Bill of Rights. Everyone is free to follow their religious beliefs. No one has any business imposing those beliefs on others.
Thus:
a. Abortion: Protecting the rights of the unborn often means ignoring the rights of the already existing, namely the mother. A fetus is a potential human being, but so are the thousands of eggs that every female produces during her lifetime. Having an abortion is a terrible thing. Imposing motherhood as a punishment for being raped or abused is despicable.
b. Gay marriage: The institution of marriage is just like every other institution; created and evolved by and for people, and subject to change and evolution as society changes and evolves. Banning gay marriage damages lives, and that is our standard for saying it is a bad thing. Saying that the purpose of marriage is love or - weirdly - procreation alone, is just wrong. Marriage has had many uses through history and different societies; the most common one has been the protection and definition of property rights. Is that what's so important?
c. Evolution: The supporters of creationism are not just against the ideas of Charles Darwin, but trying to undermine the very foundation of science and rationality. Were they to succeed, not only would they destroy the rights of all Americans to free belief and expression of belief, but also the basis of our technology and prosperity.
d. Morality: Set, fixed, final laws bestowed upon humanity by a ruling, personal, anthropomorphic deity are not the only basis for moral living. It is possible to be secular, even atheist, and to live by the Golden Rule. Having flexible moral standards is not the same as having no morality at all. Indeed, when following inflexible religious rules is used to justify murder and terrorism, it is clear that the opposite is the case.
4. Health care: There are some cases in which a competitive environment of winners and losers is absolutely the way things should run. We should have a choice of where to buy goods and services. Free enterprise is a wonderful system. There are some cases, however, when the only way any of us can be better off is if we're all better off. Safe drinking water; safe streets, reliable infrastructure; all are networked systems in which a complete reduction to serving only the individual will make everyone - even the rich - less well off. General health care is in fact somewhere in between; it should be treated as both a networked system and a competitive economic sector, somewhat like communications. The problem with the health care debate is that everyone wants a system in which they don't pay the full value for what they get.
Having the government run everything is wrong. Having the government do nothing is wrong. Finding the right balance of what government should and should not do is difficult, and constantly changing. There are no simple, hard, fast guidelines. There are no final, permanent solutions. Finding what works is the job of those who run the government, and if they avoid that job they should be removed.
5. Security: National security is a natural function of the government. It does not, however, just mean having the means and will to kill, incarcerate, and torture those we believe to be our enemies. Often, carrying out a policy of shoot (or invade) first and don't ask questions ever makes us less secure, as we create more enemies than we kill. That is what is happening in Iraq, and why the invasion was a bad idea in the conception and worse in the implementation.
Now, let's get something clear. There is no such thing as the War on Terrorism. If there were, we aren't fighting it, anyway; the invasion of Iraq had nothing to do with retaliating for 9/11, or preventing future terrorist attacks (in fact it made them more likely). What is going on is an ideological conflict between the Western idea of an open, secular society, and an ideology that has attempted to label itself as part of the Islamic religion (called either Wahabism or Salafiism) that claims that:
a. There is a fixed amount of wealth in the world, the West has stolen the share that belongs to the Harb-al-Islam, and the only way to get it back is violent action.
b. The West supports repressive, secular governments (actually somewhat true), and those regimes must be replaced by repressive, religious governments.
c. Religious faith is more important than individual rights, economic prosperity, or any set of objective facts.
The problem is that those in charge of the regime that has taken over the federal government of the United States essentially agree with the terrorists. They also gain advantages in claims of legitimacy, protection from criticism, and electoral success by perpetuating a conflict with Radical Islamism. Since neither side directs its threats or violence against the actual members of the other side, but instead kills and injures and destroys the property of innocent bystanders, neither side has any interest in actually prevailing in this conflict; they are both well served by its continuation.
But the American people aren't. The answer is neither simple nor easy. There are no magic bullets.
a. Go after the actual perpetrators of the attacks. Stop killing and incarcerating people who had nothing to do with it.
b. Stop supporting governments who are repressive and unrepresentative, like Egypt, Pakistan, and Saudi Arabia. Tell them to clean up their acts. Criticize repressive and immoral regimes like Hamas and Iran, but for the right reasons, not just because we don't like them.
c. Start sending textbooks and other school materials to schools throughout the Middle East, Asia, and the world that will properly educate their students. Train teachers in using them. This is in fact the real battleground of this conflict, and where it will be won or lost. Properly educated young people who enter a society where there are good jobs available will join the global community; they are far less likely to strap bombs to their bodies.
6. Rhetoric and lies are not the proper basis for workable policies, on any subject. Liberals do not glorify greed; nor do they excuse incompetence. Liberals believe that government plays a legitimate role in a properly working economy. They don't believe that government shouldn't work, so they don't to their best to make sure it doesn't. They must respect the electorate instead of lying to it.
The greatest threat to democratic values is unrestrained democracy.
The greatest threat to free enterprise and the prosperity it produces is unfettered competition.