(Bad) TV is no danger to people with strong critical faculties.
Of the rest, there is no use barring them from TV. Thwarting them will alienate them. And mistaken ideas are very easy to come by; they will find plenty elsewhere.
The only way keeping TV away could conceivably work is if the person was in constant contact with only good ideas, and accepted those uncritically. But in that case, if they are listening to good ideas all the time, why not just teach them to think critically?
BTW I actually think a lot of mainstream TV is quite good, and that TV has been getting better and more intelligent over time.