This is something you see often nowadays, especially on social media. Activists get some controversial policy approved, or censor some already-existing content. Yet if you protest it, you get the "dude why do you care" fence-sitters. They'll tell you that it doesn't matter that much and that both sides are silly anyway. Often these people are in complete support of said policy/censorship, but if you point it out they'll just tell you that those extremists don't represent them (because they're the enlightened "centrists", of course), and you get nowhere.
I feel like this is a big problem. How do you deal with this?
Wrong.
Dangerously wrong.
Radicals are able to bring about change precisely because of the apathetic middle. If it doesn't piss off the middle, IT WILL HAPPEN.
Therefore, it's in your interest to make sure the middle lean as far in your direction as you can.
Remember: the reason leftists don't engage in debate is because they know they will lose. The reason they don't want to lose is because they don't want the middle to see that they are wrong.
If you think the middle don't matter, you are doomed.
The left knows they matter, and they structure their every move around them. Everything leftists do, they are able to do because they have the apathetic consent of the middle. Wherever they do not have that consent, they can do nothing.