Where are you going to find the legal system under which these "slaves" will exist? This is silly. No one anywhere is advocating for "slavery on Mars". You're just arguing in bad faith to create straw men for you to burn down.
How about in the US? "Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States" [1].
However, if you are willing to regress the definition of slave to a 19th century understanding: are you being paid a wage to sell your time to build an Elysium for someone else?, do you have to wake up at a certain hour to go to work?, do you have to eat/urinate/defecate at certain hours provided by your work environment?, do you have to sleep at a certain hour to prepare for work?, do you have to work or suffer hunger -> homelessness -> death? You, me, we are the slaves already, only the whip is different. But if you own over $30 million, it's fine, you are on the internet, nobody knows you are a dog here.
[1] https://en.wikipedia.org/wiki/Slavery_in_the_United_States