Well just extremely basically, what are you gonna get when "not a democrat" forms a brand new & fully independent polity, completely outside the international system, virtually impossible to have any external insight into, not a signatory to any treaties or conventions, with no peers at all to provide any sort of mechanism for economic or humanitarian pressure and not even the realistic possibility of emigration if you're born inside it. It may not be exactly slavery as we know it historically but there are very few ways this could go I think.
Indentured servitude I believe he proposed himself actually, though I can't find it now I think it was in a twitter thread and I don't think he used those words precisely. But the idea of people taking loans for the transit costs and then working them off on mars he endorses. That could be called a few different things based on implementation I guess but given the other information we have I find it alarming. At the very least it's company town + 21st century state surveillance apparatus + the above paragraph.
And well but anyway the larger point I was making was just that his extreme political views predate covid or his daughter coming out or democrats being mean to him or several other hypotheses that are regularly asserted. If you don't find that one compelling just skip it and check the others.