So what? Democracy isn’t a sacrament, it doesn’t sanctify the government. Hitler was democratically elected. Democracy does not have moral valence as such.
But I agree that democratic government doesn't automatically justify everything. Minority and fundamental individual rights are a problem. There are a lot of tricky issues with self referentiality if you think about independence movements for instance.
A similar thing could easily happen today.
The coalition Hitler lead had around 240 of 580 seats. They didn't have an absolute majority because they weren't even near having any kind of majority. Of course a hundred of the other seats were held by communists and those went up in flames after the Reichstag fire and the subsequent ban on left leaning political organisations.
> A similar thing could easily happen today.
The last time a German government tried to outlaw an opposition party it ended up with the courts throwing the case out for involving too many law enforcement moles.
Whether someone should be allowed to campaign for genocide depends on the laws of the country. In modern Germany platforms like that are explicitly forbidden. But the laws of the Weimar Republic were more value agnostic.