Because you now did it to yourself.
First off, the communists split from the SPD, not the other way around. Second, the communists completely refused to work with the (according to them) “social fascist” SPD.
This is the correct response to the SPD endorsing Hindenburg in the name of unity (against the communists) after years of the SPD arming and approving the freikorps massacring the communists.
Thälmann who, again, was as explicitly anti-democratic as Hitler
The fact that you consider the alternative to Hitler and the guy who gave power to Hitler to be unfeasible shows that liberals haven’t changed, you still prefer fascism to working with the left.
trying to turn Germany into a second Soviet Union
The USSR went from one of the poorest countries in the world to a space-faring superpower in a single lifetime. Imagine what it could do for an already industrialized country.
Nah, better work with the fascists instead.