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?
In a rational world nobody would care what someone who claims not to care thinks, and you wouldn't have to deal with them at all. Now those kinds of comments get more attention than they deserve because the internet is full of cynical bastards easily swayed by reddit-style rhetoric. (as u/TheWestYearZero points out they've most likely had their senses dulled by degenerate consumerism)
Maybe respond with something like "Ok, thanks bye?" or "Your non-committal is noted. Now please leave so the adults can discuss this issue." Any kind of snark. It's the only emotion people like that can feel.