That's what we try to do but it depends on the situation mostly

Often that is what’s done, though you may not have noticed.

Try running your own instance, don’t moderate it, and let us know how long it took before it became a Nazi bar.

Moderating is a volunteer position, if a topic has brought a discussion to the point that multiple people are breaking community/server rules it becomes too much work.

Don't like it? Start your own community.

I can sympathize with wanting to hash stuff out sometimes, but that only really works with the assumption that the parties involved have any desire to hash things out and are acting reasonably enough to do so. This isn't like a chatroom where a mod could watch the flow of conversation and course correct it as it goes. It's harder to monitor the progression of a thread and keep an eye on things getting out of hand. And if the evidence is leaning toward, "The parties involved are trading insults and anger and not progressing meaningfully beyond that," I think it's fair for them to want to shut that down.

If you feel the subject matter itself sans fighting needs further addressing, you might be able to bring it up again in a new thread and attempt to address what you felt was left unsaid on the topic itself, while avoiding the fighting aspect of it. But I'm not a mod, so I don't know how they feel about doing that in cases where the conflict is still fresh.

Mods not wanting users to affirm another users mental health related gang stalking delusions is not “heated discussion being shut down”.

Maybe read the room of that conversation, and don’t foment its reenactment, unless you want this post to get locked as well.