Why do all adults generalize all teenagers as being rude, ignorant, technology obessed people?

Articles like this : a href="http://www.npr.org/templates/story/storyComments.php?storyId=124119468&pageNum=2&pPageNum=2" rel="nofollow"http://www.npr.org/templates/story/story…/a seriously make me think that America and the teens/parents of teens in it are going right down the toilet. Why do adults think that teens cannot be intellectual, smart decision-making, savvy people sometimes? It honestly bothers me.