More debate has flaired up over whether social science is really a science. The source of it is this City Journal article by Jim Manzi. The article is actually quite good, and highlights a lot of the empirical limitations I talk about a lot on here. Some of the commentary is less persuasive in my mind.
Razib Khan and many of his commenters overstate their case against social science as a science in this post, with many of the commenters clearly ignorant of how social science does its work, and confusing political claims with the claims of social science.
Arnold Kling, not exactly a huge cheerleader for the "social science as science" crowd, at least focuses on the original Manzi article and some of the good points that it made.
One of the frustrating things about the people who don't think social science is a science is that they're so shifty as to why. It usually starts with a methodological point, criticizing our ability to establish counter-factuals (something that is very explicitly talked about among us - this isn't a huge secret or embarassment - it's a fact of life working with the data we work with), and our lack of experimentation. When you point out the plethora of other sciences that don't experiment it jumps to another of other justifications: (1.) predictive ability (the right response: we have better predictive ability than meteorologists, and why do you blame us for not predicting recessions exactly but you don't discount geology for not predicting earthquakes exactly), (2.) ideology (the right response: ummm... yes, ideological social science is not scientific - if you're going to claim all social science is ideologically determined I'd like to see some data to support that - since I'm a social scientists of course), (3.) multiple theories (the right response: sure, but again that's just a result of the complexity of the system under study and the lack of counter-factuals. Falsification is a lot harder. You see more theoretical positions arguing in paleontology than in the rest of biology, and you see more theoretical positions arguing in biology than in chemistry - it's a function of the data, not of the "scientificness" of what we're doing).
I think there are two primary reasons why people make the mistake of thinking that social science is not a science:
1. Sentimentality: People don't like to think of themselves as objects of study. The universe can obey laws, but humans can't. We're special. An evolutionary biologist won't come out and tell you that we're made in God's image, but the residual hubris of that cosmology remains for a lot of people. We're different and you just can't study us and our social system. You can scientifically study the social systems of lower organisms, but not humans.
2. Cargo Cultism: I'm going to turn Fenyman on his head here. A lot of natural scientists are huge practitioners of cargo-cultism. If you don't do science their way - if you don't reproduce the forms of their research, then you're not scientific. The best example of this is when people say that you need experimentation to be scientific - that's cargo cultism par excellance. They often don't think about how the nature of the subject determines the form of how you approach it. I've always said social science is most like biology - and probably the paleontology comparison is even better since for the most part we're looking at historical data. Physicists and chemists don't impose the forms of their science on paleontologists because it would be inappropriate - that would be cargo-cultism. Something goes out the window when humans are concerned. The Fenyman point was really unimpressive to begin with - I think people accepted what he said just because they respect his other work and it reinforced what they wanted to believe. What was his example? People who "sit at a typewriter" and make claims that "food grown with fertilizer that is organic is better for you than other food". What does this have to do with social science? This isn't even social science - it's an anatomical/medical example, and not even an example - it's something that Fenyman just made up off the top of his head. The idea that people would cite this as an authoritative point is more than a little disappointing. It was a poorly reasoned argument on Fenyman's part without any evidence and ultimatley it was probably symptomatic of the very cargo-cultism he thought he had identified in social science.
I have yet to see a good argument for why social science isn't a science. Everything I've ever read reduces to cargo cultism or sentimentality about human beings. None of it references the requirements for a science to be a science, and if it tries to it usually fails miserably.