You should start with breeding a new kind of humans, ones that would be compatible with socialism. Of course alternatively, you could just kill a vast majority

You should start with breeding a new kind of humans, ones that would be compatible with socialism. Of course alternatively, you could just kill a vast majority of them; that's the approach most people attempting to implement socialism end up taking (viz. anything from Soviet Russia to Khmer Rouge). Alas, every time in the output you get lots of mass graves, but no workable socialism.