one bans by organising their friends and community to shun the other. the other takes control of the apparatus of the state to ban the first.
you and I have very different definitions of banning.
A Nazi punching a Jew in the face is much worse than a Jew punching a Nazi in the face. I hope you agree with this. The latter is even, arguably, good.
That's a matter of context, and raises the question of whether they're in a civil society or a war (or both at once). In principle in a civil society nobody should be punching anybody in the face and mitigating circumstances like the other person being a nazi are only details. But see Sartre's feelings about living alongside nazis in occupied France: the were very polite and pleasant, and the whole situation was tense and awkward because you're unsure of your duty in that situation - is it war or not?
There is no such thing as a civil society when one group believes the other should be segregated, enslaved, have genocide committed against them, etc. That is just gas lighting one group so that they don't know they are the frog in the boiling pot. Trying to be civil in a tolerance paradox situation just makes sure you're eliminated, but maybe just not today.
Is this a quote from Sartre, or just an interpretation? I looked for it and couldn’t find it, beyond maybe representing his “Paris under the occupation”
No, not a quote, a very poor recollection of casually reading about this. He was keen on resisting, tried to organize a group (of writers?) and made some proposals for violent acts (assassinations?) but they couldn't get it together to do anything.