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?
Then that person is (too) left wing, and is a lost cause. You can't look at the burning husks of the BLM riots, the nonstop bullsht at the elections, the tech yanking and fact checks in the election contests, and now the lockdowns and walk away thinking "both sides are the same". You'd have to be left wing to begin with to believe that.
I'm struggling to find something on the right that the progressives are justified in being mad at... and I can't think of a single fucking thing. This argument only works on sheep.
As to what to do about this, if you presume it's true that they're lying or they can't be saved, I think the suggestion to push them off the fence sounds about right. If you can make him acknowledge his partisanship, problem solved. If they were never deprogrammable... nothing lost.