Remember kids, Tankies wants to undermine democracy - same as facists.
That doesn't feel like a good argument, there are many reasons why a government descends into any of those, for one the CIA is known to disrupt any socialist/communist attempt at government and that can and did cause brutalism.
I mean if any attempt to give an alternative to the suffocating order of power is going to have to survive against the pressure of such power of course the only "successful" ones will have traits of authoritarism and strict even violent control of power itself.
Now don't misunderstand me I'm not saying that authoritarism is good or even that communism would certainly be able to lead to a better rule, I'm arguing that we don't know that because there are many other factors that can lead to the failures of a system.
Also really a blanket statement followed by generic stereotypes meant to undermine any other opinion will not lead to any intelligent discussion and betterment of any of the sides, we can do so much better.