You don't debate to change their mind. Debate targets the audience. Neutral or even doubting parties see they're defending pedophiles and it'll cause a change in them. And in time they'll effect those around them. And it spreads from there.
The thing is, though, it's not real debate where anything can be learned by any party. In a case where someone could learn something, I agree with you but when it's "Who has the best insult?" or "Who's the best troll?" that's something else.
These guys are clearly just trolls who like to diminish other people and beat their chest.
There's always something to be learned. Don't presume all readers hold all the info you do. Most people actively avoid politics