You ever hear of the idea of some act being a warning to others?
If you wipe out all known nazis, the rest of them are now aware of the price of their practices. You can then freely stomp them out as they arise, like the cockroaches they are.
No, not like roaches, because roaches have a role in a healthy ecosystem (when it isn’t an invasive species). Nazis are a fucking cancer. You eradicate cancer, you nuke it, poison or, and cut it out, you don’t tolerate it. Because if you do, it grows and spreads and kills everything else.