I'll agree people can be fiercely defensive of where they're from (there are a number of threads on GC that prove that fact). And, I think there's some importance to what is attached to the "you people" statement.
As an example, if someone said "You people in the Northeast supporting Palin," I would be a bit offended, as I can't stand Palin
I hope you see my point, though, that (to me) the context of the "you people" is important. In my mind, Kevin's statement isn't all that offensive, if only because my area of New England (both where I grew up and where I went to school) is pretty weird about the gun control issue. For example, you'd get some odd looks in Boston if you said that you were carrying on a random weekday.
As an aside, I don't know if anyone is "determined" to be on the other side of you in a situation. Personally, I don't agree with some of your posts, but I respond mostly because you're willing to debate the issue. That's not me trying to be combative with you or intentionally contrary - it's just me being honest and engaging in debate.
I agree with RC - the three of us would probably have some pretty interesting conversations if we actually met in real life.