Recently I came across a Q&A from Rav Avigdor Miller Z"L on Talk Radio and TV
Q:
Please explain why it is forbidden to go to the movies, to the theaters, to listen to talk-radio and to read secular books.A:
Why is it wrong for a man to take poison, that’s the question. If a man wants to kill himself whose business is it? The answer is, it’s Hashem’s business. Hashem says, “I gave you a body, so you have no right to destroy it. It’s not your body. It’s mine. And I gave you a mind, which is even more important than your body, and you have no right to destroy it.” So if you go to places that put garbage into your mind and put poison into your mind, that’s called destroying your mind.
“Mi’kol mishmor, ni’tzor li’bechah” (Mishlei 4-23) – More than anything that you guard, you have to guard your mind. That’s Hakodosh Boruch Hu’s command. There is nothing in your possession that is more valuable than your mind and your thoughts. Therefore when a person goes to these places or if he has a TV – having a TV is like taking a pipe from the sewers and emptying it directly into your dining room. You turn it on and a gush, a flow, a torrent of smelly garbage, filthy water comes pouring into your dining room, on the rugs. And that’s nothing yet. It comes into your head – that’s the real problem! So this person is asking a question – why are these things forbidden? Because it’s forbidden for a man to destroy himself.