against the socialists/socdems
The SDP purged its ranks of Communists to appease Hindenburg's State Police. You can't side with a party that's trying to rat you out to the cops and get you killed.
Which, again, brings us to the conservatives who held power by playing sides off each other until they misplayed their hands.
The path to fascism was paved back in 1919, when the original Communists were rounded up and executed by the conservatives.
You'll have significantly less luck delivering pizza, sadly.