Sure it's wrong to say that "large diverse group" are all bigoted. But the odds of encountering bigotry, both in quantity and severity, is higher in the south than other areas.
Also, strictly speaking, it's more regionist than it is racist, though admittedly race does play a factor. For example, I'm less likely to have a bias against a white person in Canada as a bigot than I am a white person from the US south, rightly or wrongly.
Lastly, it is funny when people of the south cry "racism" about being broad brushed as racists. To them, I say, "Hurtful, isn't it?" Rather than complain, they should take comfort in the fact that otherwise you belong to the dominant group of society and take it as a learning opportunity of how difficult it is for people who don't get that luxury.