I remember whilst doing some background reading for a seminar (no idea what the seminar was about now though

) I came across an extract that was very concerned about the future of the nation when the behaviour of its youth, especially their selfishness and 'wanting it all now' attitude, was so poor. The date of this extract? Mid 2000s perhaps the Daily Mail? Nope. The mid 1950s in some long forgotten magazine. So that 'concerning' youth would be the same people who are now decrying the hoodlums of today then...
I also agree with you last point that people remember bad interactions more than they do neutral ones. Who remembers walking through a university library and seeing dozens of students working hard? But students having too much to drink and getting themselves into trouble that's easy to remember.
I also think the media play a part in this because there are sections of society that want to be told the youth of today are terrible and wasn't it so much better when we were young. It also makes a much better story so will sell more papers/grab more audience share. Telling us how students today work as hard (or even harder) as they always have? That does not make for a good story.