I think that we physical scientists possess a bit of hubris when it comes to our perceived understanding of nature. Its roots lie with the view that the laws of physics govern everything and the rest is just details. Unfortunately this hubris is shared by many of my physicist, engineering, and chemist colleagues. My issue is not, however, with their assurance that nature can be reduced to a set of relatively simple laws; rather it is with their perception of the social and some natural sciences as pseudo- or unscientific.
I witnessed this type of hubris many times as an undergrad where fields such as political science, economics, and sociology were labeled not as social science but as humanities (I went to an engineering school). Most of my classmates enjoyed their required classes in the humanities since they were a nice break from their challenging engineering courses. And perhaps this is the point where the hubris begins: as a belief that the humanities are somehow "easier."
It bothers me when I hear some of my grad school friends roll their eyes or make the quotation mark gesture with their fingers when they sarcastically refer to work in the humanities as science. This perception of the humanities as unscientific is outright false when they are weighed against the logical structure of any science. Hypotheses are formed, observations are made, and conclusions are drawn from the observations and prior knowledge, just as in the physical sciences. If there are differences, they lie not with this structure, but with the scales of measure involved; the physical sciences tend to employ more quantitative measures than the social sciences, but this by no means makes one field more scientific than another.
On a positive note, I don't see this arrogance in most of my grad school friends. I just wanted to explore why a few of them marginalized the humanities as a science so I could better defend my position in the future.
And if I'm being hypocritical through my continued use of the word "humanity" and not "social science," I only used it because I simply could not think of any better word to use. Ultimately, it's all science to me ;)