If you don't allow the Nazis then there is no opportunity for people to refute them in public. Just think about it. You have to have faith in that open conversations and debate will bring the light to even the darkest minds. If you cut them out completely then the following will / will not happen.

No one will ever encounter what they think and begin to ponder it as it's actually presented and then dedicate themselves to refuting their ideas on their own terms, in terms they themselves accept as valid.

They will never encounter an intelligent counter to their beliefs that starts to work away at those beliefs.

No empathetic person can ever be given a chance to divine what they're really worried about / afraid of/ hopeful for and separate those things from the Nazi ideology which currently serves those needs.

You have to believe in the power of ideas and words to change minds and behavior. What else is there? War. Violence. Killing.

The whole point of free speech is the bomb defuser gets to examine the bomb, learn about it, be with it. think about it, sleep on it, dream about it, absorb it, grok it .... then finally diffuse it in a fit of inspiration and genius. This is what great writers do. This is what great thinkers do. But you can't cut them off from engaging with the raw material of what will later be their ultimate triumph.

Censoring ideas is one of the first things the Nazis did. That's because they know they can't withstand all minds which may come at them. Ditto Critical Theory fascists and fascists of all types. They amputate inquiry and speech because they know, deep inside themselves, that a better mind than theirs with clearer thoughts will eventually come along and they'll be defeneseless against them.