Social science is also science. I don't think sci-fi has to do with technology or biology all the time. In TOS there is a lot of culture stuff, there are a lot of philosophical issues taken up. There are also ALOT of ethical issues being poked at. The show often seemed to me to want to provoke people by speaking of how violent and savage and simple human beings are. If ST isn't sci-fi I am sure the same could be said of all sci-fi series. B5 could be called a series about politics and war in space.
My point is, you have to know how you define the term sci-fi first. Does sci-fi only entail robots, clones and space ships? Or do aliens, space travel and social science enter into it? IMO Social science seems to be a major thing in all sci-fi works, and social science plays a huge part in TOS.