It's not all dreck of course: there is the Hitler History Channel, the Hitler Military Channel, C-Span (especially its Book Notes), and a few others.
An example of outstanding TV is Rod Serling's Twilight Zone, which ran from 1959-1964. Comparing a series like TZ with trash like The Sopranos, Sex and the City, and recent 'reality' shows, one sees the extent of the decline.
Serling knew how to entertain while also stimulating thought and teaching moral lessons. Our contemporary dreckmeisters apparently think that the purpose of art is to degrade sensibility, impede critical thinking, glorify scumbags, and rub our noses ever deeper into sex and violence. It seems obvious that the liberal fetishization of freedom of expression without constraint or sense of responsibility is part of the problem. But I can't let a certain sort of libertarian or economic conservative off the hook. Their lust for profit is also involved. Not that liberals are not just as driven by lust for profit despite their official stance.
What is is that characterizes contemporary media dreck? Among other things, the incessant presentation of defective human beings as if there are more of them than there are, and as if there is nothing at all wrong with their way of life. Deviant behavior is presented as if it is mainstream and acceptable, if not desirable. And then lame justifications are provided for the presentation: 'this is what life is like now; we are simply telling it like it is.' It doesn't occur to the dreckmeisters that art might have an ennobling function.
Companion post: Some Things I Look for in a Movie