I’ve known some pretty nasty middle income level kids with fowl mouths along with upper and lower income level kids also. I do not think you can judge the kids these days strickly going by what income level backgrounds!
I had a kid at my house one time and he insulted me - twice. I put his nasty butt in the car and drove him directly home. Wow. What a nasty piece of work that kid was. He was one shocked kid when I escorted him to the door and told his mom why he was home so early.
It’s not a matter of judging them, but of expecting more from them. Kids who grow up in comfort and with everybody doing everything for their happiness should be kinder than ones who grow up having to fight for everything they get.
But they’re not, because their parents don’t teach them anything. And the parents probably aren’t very nice either.