"but freedom of speech let's you defend yourself and convince people!" he will, understandably, argue.

No. That'd be great. That'd be amazing.
People have cognitive biases. They have ideologies they're ready to kill for even if you empirically prove them wrong. Religion is a perfect example.
People aren't rational machines and will burn you at the stake if that's what they want. Free speech won't save anyone against someone that doesn't want to understand.