I thought it might be worth adding some further thoughts to clarify. I don't think that every family that has a television is necessarily doing harm to their children. Many such as Jackie Parkes, or Francis (cf. combox) use the TV responsibly and with vigilance. But I do want to assert that it is perfectly all right for a family to choose not to have a TV. This is called into question by those who want to say that the television is an essential part of our culture and that a family, or an individual, is missing something important by not having the TV at home.
Nor am I saying that the electronic item itself is an evil. It is possible to view EWTN or good films without falling into the trap of channel-hopping and leaving the set on all the time. However, there are other ways of obtaining such content: via the internet or, in the case of films, by using a projector. A fairly cheap projector is quite suitable for an average living room.
My principal concern is that many families are subjected to a form of cultural bullying. If they make the perfectly reasonable choice to do without a television, they are sometimes cast as misfits or social pariahs. It sometimes disturbs me how many conversations (even among clergy) focus around "that programme last night".
In Britain, we have the particular problem of the licence fee. BBC Resistance quotes M. W. D. Kimball of TV Licensing Customer Services on the conditions under which you need a licence:
"A television licence is legal permission to install and use television equipment to receive or record television broadcast signals. Under the Broadcasting Act 1990, you need a television licence to receive or record television programmes. This applies if you use equipment to receive or record BBC 1, BBC 2, ITV, Channel 4, Channel 5, satellite, or cable programs. If you are watching 'Sky', or any other satellite service, controlled from within the UK, you must have a television licence."Note that if you watch a satellite service that is not controlled from within the UK (such as EWTN) you do not need a licence.
Although it is a legal requirement to have a licence to watch, for example, SKY, the revenue from the Licence Fee goes to fund the BBC. Many of us object strongly to having to fund the BBC in this way and this adds a further incentive to get rid of the TV or at least to arrange things in such a way as not to be legally required to pay the Licence Fee.
"Satan's black box?" Some people find this kind of description extremist. I would say that it is legitimate hyperbole. Satan certainly has benefited from the corruption of children through unsupervised television watching, and the (now documented) bias against the Catholic Church and the pro-life movement.
Is the internet just as bad? It can be worse, of course: many boys and men have become addicted to pornography because of its easy availability on the internet and there are many other problems besides. Some religious orders make a point of not using the internet and I respect that. It can be helpful but I would not say that it is essential. At the moment, we are able to use it to circumvent the bias of the mainstream media and to promote Catholic teaching.
The difference, I think, is that the internet is basically pull technology. You decide, you choose. TV has become much more like that with the proliferation of channels but it is very limited by comparison and the barrier to entry for producers is much higher. So for the moment, I'm happy to use the internet but not watch TV. It is not part of my intention to say that everyone should do that, just to encourage those who are standing at the water's edge wondering whether to plunge into a TV-free life. It really won't hurt!
(BTW - I found that graphic of the broken TV over at The Daily Yada: TV-Free August. The (homeschooling) family agreed to do without TV for a month. The children pointed out that Mum did not watch it anyway so it would not be a sacrifice for her. She had to give up sugar!)