It's all about the law
Thiel et al think there's a demand for R&D space near, but outside of, the USA in international waters where their work would not be subject to the US legal system. The Economist piece mentions a few of the major design & engineering issues that would would need to be overcome. Many of these posts raise other issues that would be moot because these seasteads would be commercial operations providing space for other businesses - ones that are, legally, not the same as any companies incorporated in the USA or any other nation.
Then there's the gratuitous political rants, but apparently some people will use any opportunity to vomit another 1.
