Roko is of course begging the question, and the premise he is wrong about is that there is a sizable population willing to relocate to a floating iceberg, instead of living in an existing country.

Consider what the proposed citizens have to consent to:

• paying for the R&D required to implement the technical solutions Roko envisions, along with the continued higher maintenance costs
• paying higher wages for the people who are supposed to do all the boring menial jobs in this floating city, on par with existing cities
• paying higher daily cost of living for everything from food to building supplies to luxuries to entertainment that have to be imported
• being at the mercy of "legacy governments", many of whom possess navies capable of everything from interdicting the food supply, to literally undermining the city from below, to actual assaults and airstrikes
• paying higher prices for insurance of their lives and dwellings and possessions because of all the above

Amusingly the solution for a libertarian city is a megastructure project probably only a rich nation is prepared to pay for.