Look at the outcomes as you said millions dead between both systems. Both used a totalitarian government to collect all the power to a central organization. Sure the stated goal might be different but they act like all other political organizations they collect power.
The argument you're making is like arguing protestants are anti catholics because they fought each other
Or Sunni and Shiites
The arguemnt against it is that it's all the same unless you do skmehting systematically different like free markets. Economic decisions aren't made by political methods. Not which flavor of political methodology is being used.
The rest is just theater.