The thing is that they actually probably would have.
For a bit.
Nazism was very much a centrist reaction.
The SDU were the socialist republicans of what passed for being the right wing in that country, at the time. The commies referred to them as being "social fascists" if you can believe it, and the German commies were both incredibly influential and incredibly violent.
While a lot of national socialism seems like ultra-lefty shit it was centrist for where Germany was politically at the time.
To the right, a socialist party that's got shit policies and is destroying the nation, to the left, a communist party that's got shit policies and is destroying the nation.
Doesn't that just make the average, normal, centrist person want to throw all democratic ideals in the trash, elect an Emperor and violently expunge all radical elements from their society?
History has proven on multiple occasions that these people would be glad to punch someone in the face for very little reason. They would have punched Nazis in the face had they been around during Nazi Germany; I have no doubt about that.
They would have gladly punched a lot of Nazi sympathizers, neutrals, people who questioned them or people who didn't claim to be avowed communists as well.
There's a reason why the Germans were so okay with the violence of the browshirts. There's a reason why executing tens of thousands of agitators, and sending the rest to labour camps was very popular.
No one likes idiots who go around committing acts of violence for the sake of their politics. The anti-fa folk tend to lose fights, but they have no problem fighting people or committing acts of vandalism. They certainly would have done the same at the time, and paid a dire price for their stupidity.