To his point: if not "discuss", what is the correct approach against fascism? war and murder? dismiss it, try to "cancel it" without giving any arguments so it can continue to fester on its own and keep growing in opposition?

To me, fascism is a stupid position that doesn't make much sense, to the point that it falls on itself the moment you "discuss" it.

I would have expected that it would be the fascists the ones unable/unwilling to discuss their position, since it's the least rational one. So it's certainly very jarring whenever I hear people jumping to defend against fascism while at the same time stopping in their tracks when it comes to discussing it. Even if those unable to reason might not be convinced by our arguments, anyone with reason would. Rejecting discussion does a disservice, because it does put off those willing to listen and strengthens those who didn't really want an argument anyway.

Like flat-earthers, they should be challenged with reason, with discussion. Not dismissed as if it were true that there's a huge conspiracy against them. Whether they listen or not to that reason, dehumanizing them and rejecting civil and rational discourse would play in favor of their movement.

Stating "genocide is bad" should NOT be a statement of faith. Faith is the shakiest of the grounds, if we are unable to articulate the specific reasons that make genocide be bad, then we are condemned to see it repeat itself. So, I'd argue it's for the sake of the victims in Auschwitz that antifascism should not be turned into a religion, but into a solid and rational position that's not distorted nor used willy-nilly.