I have a solution. I'm implementing it. If you have an improvement on my solution, I'm all ears. If not, kindly just let me keep doing what I'm doing.

I don't pass judgment when asking if the person is sarcastic. I'm only hostile once they refuse to clarify. (Being sarcastic in response isn't clarifying. If a person missed the sarcasm the first time, doubling down makes you kind of a dick, regardless of what you're actual motives are). That hostility is, by design, asymmetrical. Because I'm not targeting the person making a stupid joke. I'm making nazis and fascists unwelcome. I can't be charitable because doing so, again, makes the space more welcoming to those I don't want to be here.

Making nazis feel unsafe is the only way to keep them out of a space. You can't continence any of them, regardless of how "respectful" they are. Social cohesion is not made from a lack of social tension, it's made from trust that those around you aren't hostile to your existence.