You’ve got a lot of replies, so this probably isn’t needed, but debate and persuasion only works if the views they hold are reasonable and if they came to those views through reason. It also legitimizes their views. Often “debate” is used as a tool to appear like they’re the more reasonable person by being the one who always asks questions, but they never answer anything. They always attack and they don’t defend any view (because they are not reasonably held, just useful), so they look like the more powerful persuasive point of view.
Basically, argument only works with reasonable people. The alt-right generally are not reasonable people and will use your arguing to make you appear stupid and them appear powerful to recruit more people. Don’t argue with the alt-right. Only humiliate them in the hopes others see how bad they are.