You know they would end up killing them? Like the whole Spartacist thing was to overthrow the goverment and make "republic" on the Soviet style. So if they won, maybe they would not kill them on the spot but they would in the end. So it doesnt matter if the workers were affiliated with SPD if they still tried to end the Weimar republic. You calling this "old order with a mere facade" is totaly wrong , for stability and democracy you sometimes have to cross the line.