Heck, there's stories of people from particularly poor backgrounds getting insulted for trying to get a college education.

I think this is still "explained" by "don't act weird" to the extent that any of these theories explain anything.

Maybe, but the same kinds of reactions happen even when trying to, say, quit eating donuts.

knb's explanation also covers this one. Also, the only time I recall something like this happening is when my high school friends disapproved of vegetarianism among males because it is unmanly. "The egalitarian instinct" is not a good explanation for that behavior.