This very good thread reminded me of a book I have somewhere in my library, "Four Arguments for the Elimination of Television" by Jerry Mander. The writer had experience in the advertising business before becoming a non-profit advocate.
Amazingly this book was published in 1978! Way before the expanded cable TV offerings of today with the multi-channels and the streaming of varied types of entertainment (movies on demand, specialized shows, etc.).
The writer thought that the bad effects of TV were inevitable - so we can't really blame a few bad apples that, if gotten rid of, the bad effects could be eliminated. A provocative argument to be sure.
Personally I do maintain TV but not cable, as I agree with other posters who refuse to pay mega-bucks per year to get shows riddled with commercials to the same (if not worse) degree like network TV.
Ads could be tolerated but not as much as we are being bombarded with: it used to be you got 4 minutes of content and 1 minute of commercials; now it is down to almost 2 minutes of content for 1 minute of commercials. WHY?? Because the networks found out that by gradually increasing the ad content people would not abandon TV? Unacceptable.
What it they continue adding ads little by little and end up with 1 minute of content per 1 minute of ads? Unthinkable? Just you wait.
On the plus side, there is interesting stuff, and I think that over time you can get most of the interesting stuff that might appear on cable through the network channels (with heavy emphasis on public TV - PBS in the U.S., BBC in the U.K., etc.).
I think that network TV does have every now and then entertaining shows, and PBS has useful educational material.
I see some say they don't watch TV but then get TV-content via the Internet - to my mind at least this is semantics, if you watch TV content via internet you ARE watching TV! The medium just differs a bit (and you in fact can avoid commercials LESS via internet than you can with regular TV and while using a DVR (like Tivo). It's only temporary that you are being offered fewer minutes of ads via internet, this too will increase gradually over time.
Also to consider is whether substituting internet for watching TV is really making a fundamental change. In a way it is too early to judge, but it is possible that over time bland content from well known websites will come to dominate (even forgetting the part where people watch TV-content via the internet).
Also, there is the risk that people will gravitate to ever more narrow interests and pursuits - or to social networks of little or trivial value (twitter?).
Overall, I think TV can be tolerated if cable is not used and if one focuses on a few selected shows of good entertainment or educational value. But it should be limited and not too much expected out of it, other sources (books....) need to be accessed regularly as well.