Some of the shows are as you describe, and focus on the reality and drama of things gone wrong. But others have more of a "How To" flavor.
I watched a show on DIY yesterday that made my head spin. A host was showing a young couple how to remodel their bath. In 30 minutes they installed a heated tile floor, installed a steam generator for the shower, installed a mortar bed pan and tiled the steam shower walls with glass mosaic tile.
While it was funny watching them do just about everything wrong, it struck me in the end as incredibly dangerous. They skimmed through showing the happy couple and host having a ball. What you didn't see, is just about every important detail necessary to make a bathroom beautiful, lasting, and
safe.
They even hooked up the steam generator themselves.

There are professional subs I wouldn't trust with that. No mention of T&P, drainage, steam line placement and pitch... Nadda. Just a few shots of the host showing the HO how to sweat copper.
As I said, with the right lighting, production values, and a camera that pans around without focusing too close--it's the materials you see and not the crappy way they were installed. The bath actually looks nice.
Sad. Sickening.
So what's a homeowner to take from that, on the "DIY" network no less?
"Hey, they made it look easy--I could do that."
They may not want to attempt it themselves--but the perception of the trades is still damaged. We've all come across the prospective client who doesn't want to pay market rate for our services because they fancy themselves good enough to do our jobs as well as we do.
I have to disagree with you Chris because most homeowners on those shows are really clueless. I understand in theory what you are saying but I doubt the average homeowner has what it takes to complete from start-to-finish even the smallest of bathrooms. There's lots of cooking shows too and that hasn't hurt the restaurant business. People still go to the movies too even though they can stay home and watch DVDs.