except that Jewish Germans weren't calling for the genocide of Christian Germans. The premise was a lie, constructed to scapegoat the Jewish population for the Germans losing the Great War [1].
Banning people from calling for genocide doesn't apply to governments committing genocide to back up a lie. That's a pretty obvious distinction.
You made my argument for me. When those in power use the justification above and the justification is not based on reality, it has disastrous consequences.
It's not a valid justification, and authoritarians don't care about objective reality or rationality.
when authoritarians get into power they can do whatever the hell they want. That's why the point is to stop that happening in the first place. Hitler turned himself into a dictator pretty much immediately after (possibly staging) the Reichstag fire and declaring a state of emergency.
The whole point is to stop people like him getting in in the first place, and you don't do that by making calls to genocide viable.
Hitler was elected based on the premise that he would save the German people from destruction, the exact justification you excuse, not simply because he hated Jews.
and making it illegal for parties to call for genocide would've helped his campaign, how? It doesn't necessarily harm his campaign as he could/did just dogwhistle instead, but it certainly wouldn't help it.
FWIW Hitler wasn't the example I was thinking of when using that example. He didn't AFAIK explicitly call for genocide but he did dehumanise Jewish people with propaganda.
And this is how fascism starts