I agree with you, Mr. S. Whenever I was confronted with these challenges as a teacher (and believe me, it was frequently), I had to search myself and wonder if the values I was used to and most middle or upper middle class white people, hence teachers, have were not the same as the ones my kids/parents had. Most of the time, the answer was no. This does not mean that kids should be allowed to threaten anyone at school or disrespect teachers. But, if I dug a little deeper I would see the situation for what it was. Sometimes, all I could do was wait for the end of the year (or in my case, 2 years, because I looped with my kids), but other times, through a lot of work and help from others at my school, we made tiny inroads with the parents and/or kid.
I think it would be really hard to live through a demographic change at school. It's like the whole world changes. The last 2 places I taught were challenging because we had the kids who lived in 500k houses and also a large group of kids who were immigrants or from a minority culture. Because so many of these kids had no social boundaries or rules at home, for whatever reasons, we made social/emotional learning a huge part of the curriculum, with the Responsive Classroom program (it's called something else now). That, and community service at every grade level forced the kids to focus on something other than ME, ME, ME. The Responsive Classroom was a venue that made it possible to have the time to teach the social skills and manners that so many don't get at home. It wasn't a big chunk of the day (20 minutes 3-4 days a week), but I couldn't start my day without it. That morning handshake and sitting down and doing an academically focused activity, and sharing our outside lives broke down a lot of barriers. When my son enlisted, I had the worse group of kids I've ever had. But, when I sat down in our morning meeting and told them what happened and how upset I was, they came through. They helped me make it through the days ahead.
Was it perfect? Of course not. Teaching is the hardest job anyone can do. In fact, I can't believe I did it for 30 years.