There's an issue when talking about people who are near the center of the political spectrum, and I think it lies in a nuance between the terms moderate and centrist.
A moderate refers to someone who holds political stances that happen to be near the average of the prevailing clusters of opinions on each side of the issue (within the contextual time and region). My impression is that "centrist" has a different connotation, and a worse one in the way that many -ist terms tend to have negative connotations at least among intellectuals who promote freethought: for instance, Darwinist and evolutionist are mainly used by those who oppose the theory of evolution because the -ist suffix suggests ideological adherence rather than something more scientific-minded (I've always tried to avoid calling myself an evolutionist for this reason).
Similarly, calling someone a centrist seems to suggest that they're adhering to a meta-ideological agenda, one which some people no doubt do pursue: that of choosing, as a rule, stances which reflect the average of the opposing sides. (I've certainly seen people accused of being "radical centrists" if they're perceived to take this philosophy too rigidly.) There are possible defenses for this: one could take something akin to majoritarianism as a guiding light, for instance, where they figure that humans as an overall population tend to be correct about things on average -- sure, we differ widely on certain issues, but the number of people too far on one side is always going to be balanced out by the number of people too far on the opposite side. I personally find this an extremely doubtful assumption. I also tend to think that some people use it as a cover for laziness: there's no need to research issues on your own in an open-minded manner if you can just take the average of the opinions you see around you as the formula for the correct stance.
So according to my interpretation of centrism, it's something I (and I think many others) view unfavorably. But it would be an unfair to conflate this with someone who arrives at their opinions in a freethinking way without reference to the major political parties' stances or how they perceive the camps that most other people belong to, and finds that their views happen to lie near the center on most issues -- in other words, centrists should not be confused with moderates. And I suspect that a lot of hostility towards moderates comes from such a conflation.
