The thing is racism and white supremacy don’t respond to debate, because they’re not based on logic to begin with. Both ideologies are based on ideas that can easily be disproven with even basic research, but that people who subscribe to them either are unwilling to hear information that counters them or don’t care that they might be wrong. You can spend hours telling a racist that their views on “race realism” are provably incorrect, but that doesn’t matter if they just reject any information that doesn’t confirm their worldview. Moreover, the fascist or racist can just keep on throwing out shitty untrue claims until they hit on something that their opponent doesn’t know how to address. Even if the fascist/racist’s claim is still inaccurate, and even if they’ve been proven completely wrong dozens of times up to that point, they tend to walk away from that final gotcha exchange feeling victorious, leaving them reaffirmed in their beliefs.
Adding to this, publicly debating racists and fascists creates a real risk of spreading both ideologies. By having a public debate, you implicitly signal that this is an issue with two potentially legitimate sides, when that isn’t the case. It would be like having a serious debate on whether the earth was flat or round, it only legitimizes the side that deserves no legitimacy. Adding to that, public debates give viewers the impression that racism/fascism might be relatively normal parts of society, or at least more acceptable than they had thought. This allows hateful speakers to begin pulling more people to their cause, people who might be prejudiced but otherwise never would have done so.
So what do we do about fascists and racists? We deny them a platform to speak to the masses and socially reaffirm that both ideas are unacceptable. Bigotry thrives in mutually supportive bubbles, where hateful people reinforce each other’s hateful beliefs, and dies in isolation, when people are constantly challenging that hate. If someone still wants to publicly espouse hateful rhetoric they can, but I would bet you the world that less will do so when they aren’t able to see their beliefs publicly presented as having legitimacy or when they’re not able to easily connect with groups of similarly hateful peers.