"Debate works" and "debate doesn't work" people are both right, because they're saying fundamentally different things.
1) "Debate doesn't work" because, by and large, you're not going to convince a racist to stop being a racist with rational arguments: racism comes from an irrational place untouchable by logic.
2) "Debate works" because it exposes racists as the irrational, logically bankrupt people they are, and when these people have an audience in the millions, this is important. There's an idiom in Spain that's all about this, "darle cuerda para que se ahorque" (lit. "give them rope to hang themselves", where "give them rope" means letting them talk). The more a racist tries to rationally discuss his ideas with non-racist, the worse their public image becomes for everyone but other racists. Leaving them unchallenged allows their audience to assume the best of them, which is actually what's happening with JonTron.
"Debate works" people mostly agree with point 1. "Debate doesn't work" people might disagree with point 2 on fears of giving them exposure and legitimacy, but those are things they already have in the eyes of their followers, and the only way to strip that legitimacy away from them is forcing them to expose their hollow, flawed world views in detail.
There's another discussion that's often brought up in tandem, which is "deplatforming works". I think everyone (except perhaps the most radical defenders of free speech at any cost) would agree with this, but this is kind of an orthogonal discussion to the above. Deplatforming is obviously the ideal solution, and has been proven once and again to work (if you disagree with this, you're either misinformed or a troll, sorry), but for someone to be deplatformed, they have to be unambiguously exposed as a racist. That's where debate can help.
