It is a tricky one. Most TV is basically awful. It is mass entertainment but French, UK or whatever the case, special or secondary channels provide fantastic programmes. We have children, they dominate TV viewing. When it comes to TV for them then the English language offer and diversity is by far the best, in fact whilst we encourage our bilingual daughters to watch French and occasional Italian or German channels, the UK choice tends to win over hands down.
Peter's question is a good one, but answering it is one of those things where it can come out subjective in some people's minds or patronising in others. In the past people have said how watching French TV only helps learn the language. True. However that does not excluded keeping in touch with one's first language, especially since it may be the more relaxing part of TV use. Each country also has strengths. Now, for instance, I like good crime series. I find that much of Europe is now 'infected' with CSI, Mentalist type series, repeats galore at that, and domestically made ones are on the decline. So I watch German ones, der Alte and Tatort have always been good and around for years. Nowhere has any to quite compete. I must say I shrivel up when my OH watches Italian TV, I tend not to hang around too long.
However, I think French TV has excellent programmes, Arte is great, put that in a pick and mix with other services and why not use two languages? Andrew has a good point about getting English language TV for his young to get some language support, so let us not only think in terms of adult viewing which I suspect most people are. Anyway, people might want to follow their Corrie or whatever, so why not? There are no hard and fast rules.
As for Peter's point about sport, it is actually good. UK TV is generally far more diverse than any other for sport and I also find that when watching international football and rugby, for example, commentaries are far less biassed toward the home nation in particular. I must say how annoyed I have been by French commentators all but accusing a UK team of cheating after a brilliant try in a couple of matches, bad enough but to then go into a discourse about how if would have turned out if... I watched an Italy versus France game that began with the commentator reeling off all the faults the Italians had brought with them then saying how they were no-hopers against France a couple of seasons back. That deeply annoyed me. They are not perfect but UK presenters, including Scots, are less inclined to do that.
So, if we have a choice and a preference why not. However, living on an 'island' of only English language TV, newspapers and all is so often a self-defeating exercise I would always advise against. However, it is choice so live and let live is the bottom line.