Say you're an Evil Overlord. A successful one, to boot. What's the #1 most dangerous threat to your Evil Empire? No, not The Hero or the ancient crystal sword, the only weapon that can destroy you, but hope. Specifically, hope in the downtrodden masses that your reign will end, that resistance isn't futile, and that helping the hero (or outright rebelling against you) can end your reign. So naturally, every Evil Overlord will periodically say "Make An Example Of Him!" and have a defiant peasant (or better yet, the captured hero!) killed in a messy and public way. Or given a Fate Worse Than Death. This may involve a little genocide (which inevitably backfires, if not Nice Job Breaking It, Herod!), the destruction of churches and monuments, and probably the assassination of anyone daring to raise the spirits of others. For this reason, artists, philosophers and their collective works are also frequently targeted. That it also serves as censorship is a neat little bonus. Sometimes though, characters who aren't Evil Overlords engage in this. This is usually a character who has given in to despair and doesn't want to be confronted with a positive point of view, and would rather the hope-bringer just shut up and die. A particularly successful Evil Overlord will be able to make his subjects police themselves in this way through fear.
Hello, Unknown Troper. You'll need to get known to lend a hand here.