David Sirota and Nate Silver are having something of a pissing match, with Booman taking a more reasoned look at the issue. It's pretty obvious that a lot of the back and forth is personal -- the two really seem to dislike each other -- but there is actually a fair amount of interesting material in the posts. I want to start with the duality that Nat Silver talks about here:
The definitions of the terms "liberal" and "conservative" have been the subjects of much debate in contemporary American politics. But it has become increasingly clear that the term "progressive" is equally ambiguous, and is associated with at least two relatively distinct philosophical traditions. Although these two "progressivisms" share common ground on many (probably most) issues, they are at loggerheads on some others, as has perhaps become more apparent since the election of President Obama.
Now, if you read the entire posts, it is clear that Nate thinks of his side of the divide as superior and that he isn't going out of his way to be fair to the other. The list of attributes he assigns to the "radical" side is not the most flattering collection of adjectives ever assembled and, in many case, are unfair. The fact that he calls his side rational and his opponents radical in and of itself displays a bias. But Nate is correct that there are two distinct branches of through on the left. I have always thought of them as the "liberal" and the "leftist" side, but reformer and revolutionary work as well. And, oddly enough, I have always thought that To Kill a Mocking Bird is a wonderful example to highlight the two. Spoilers follow, though, really, didn't you take a High School English class?
In To Kill a Mockingbird, the hero of the story defends a black man in 1930s Alabama from accusations that he raped a white woman. The accusation are obviously, almost comically so, false. The lawyer does receive some amount of low-grade harassment and social rejection because of his decision to adequately defend the accused (though when forced to choose between protecting the false accuser or the lawyer, the town's power structure chooses the lawyer). The black man is unsurprisingly convicted and later dies in an attempt to escape. The book holds the lawyer as a hero, a good man who did everything that could possibly be done to save and innocent man. That is the liberal interpretation of the book. A leftists would see the book differently.
The black man is still unjustly convicted and still dies. The lawyer walked away from him the moment the trial and did nothing of substance beyond that point to attempt to rescue him form prison. The lawyer worked the system as best as was able to, but when that system failed the lawyer accepted it and moved on. The lawyer may have good intentions and may even be a good man, but when presented with a moment in which the system turned to destroy and innocent, he did nothing. Whatever good qualities he may have, the lawyer was no hero.
I don't know the two men personally, but I suspect that Nate would favor the first interpretation and David the second. The tension on the left has always been about how far you have to go to change the system. Does it need to be torn down, or can it be reformed? Neither position is intrinsically superior. FDR was a reformer, MLK was a revolutionary. Waiting for reform means that people who don't deserve to suffer are going to be made to suffer. Reformist who forget that come off as smug, elitists more interested in their own comfort than their own ideals. Tearing the system down means that, in the time between the old system and the new system and due to a lack of experience and expertise many people are going to be made to suffer who otherwise would not have. Leftists who forget that risk coming off as smug, uncaring bastards interested in people not for themselves but as nothing more than a means to an end.
The question right now in America is one of reform versus marginal restructuring: should the existing neo-liberal economic and political order be allowed to stand if it is reformed, or should the US turn to a more social democratic, labor friendly, fair-trade alternative. Objectively, the difference between a reformed neo-liberal order and a social democratic order are not that great (which is not to say they are insignificant, just to point out that historically speaking they are first cousins rather than the different families of capitalism and communism) but they are proxies for this larger argument about the direction of the liberal left, so expect to see much more of this in the next few years. Which will probably be a good thing -- the more they fight, the more likely it is that the liberal position becomes the "center" in opposition to the leftist and radical right positions.