Why is it that it seems that more an more people are becoming cruel and desensitized?

im 19 and have come to a firm conclusion that peoples manners are going to the trash can. i cant tell you how many times i hold there door open and get no thank u in return or even have the door slammed in my face. kids have no problem mouthing off to there parents and even elders. and i think even some middle aged people are getting in on the act. people watch shows were other people are humiliated and laugh at it. all im saying is whatever happend to being a lil curdious to your fellow american(and for all those who are not in america u know what i mean) so what do you think? (and im not saying everyone is like that but it seems like the majority has gotten like this)