The point is that you should argue why you find "dictatorship of the proletariat" unethical and not confuse the difference between ethics and economic viability.
There's definitely philosophical problems with communism and communist thinkers of various sorts. No denying that. But the screwed up crappy attempts at something like communism simply don't invalidate all of the principles which must be considered separately.
Basically, if you run a shitty version of an experiment, you don't get to then claim you proved the null hypothesis. It's one thing to say "we can't afford to experiment" and another to say "we had [shitty] experiments and so now we can conclude things."
You could argue for no more trials and still accept the fact that we never got any good trials from which to conclude enough about the real principles.