if you want to use the sentiment expressed in this post as an argument for marxism being good, which seems pretty transparent in this case, then that same sentiment being used to justify eugenics isn't a good thing for said argument
i'm not that concerned with the precise definition of "opposite", but i am concerned with whether or not the post's logic is sound
i've given two examples where i think the average person would come down on the side of "let's do some eugenics" until being told "haha you just agreed to do some eugenics"
the problem with the post is that if you boil it down, it becomes "things that sound good on the surface are automatically good", which doesn't hold