Generally speaking the benefit of Seasteading is that a single Seastead will consist of crowd that has more homogenous needs than current countries. By seperating the communists from the anarchists and both of them from the social capitalists, everyone can have their ideal world to live in.
The gains made in happiness for humanity depends on how much said crowd suffers in the current countries.
Now, which groups suffer the most, because they have the most unique needs? I think physically handicapped people are very well suited for their own Seastead. Not only do they live in systems that are not designed by them & for them. They also have a lot of potential. I proposed this idea to other people before and it should only happen if those groups WISH to live there instead of where they are now. By no means should this end in forceful deportation.
Also, if you have extensive contact with physically handicapped people feel free to challenge any of my assumptions.
First I want to make a point about ‘disabilities’ (I am sorry if that is the wrong word, I am no native speaker). Nobody is considered to have a disability because they cannot fly. That is because nobody can fly. So what is seen as ‘disability’ is always dependant on the environment somebody lives in and the abilities those people have.
Blind or deaf people as well as those with the need for a wheelchair have their needs largely ignored by society because they are a small fraction of the population. They need elevators instead of stairs, traffic lights that make sounds and computers with no display. Often they depend on the help of others (to move around, get money etc.). Not because they are inable to do so, but because often the world they live in makes it very hard or impossible.
If there was a Seastead with e.g. only blind people, the government and society would adjust so well to their needs that being able to see might make it difficult to live there. In this case, I can see carefully designed infrastructure that relies on tactile or hearing abilities. I can see the government put extraordinary effort into the development of human-computer connections that do NOT rely on eyes. I can further imagine that this city will specialize in those things that blind people are better at. I am not 100% familiar with the science, but as far as I know blind people have a better sense of touch, better hearing abilities and increased memory. So not only could they be productive people working for their own freedom - they could outperform normal people in certain areas.
This intensified specialization and bringing together of people who are alike can propell mankind as a whole forward because likely there will be discoveries and achievements that only certain people can make. Maybe deaf town will be known for the invention of a new way to communicate more knowledge through sign language than speech (#TheArrival). Maybe blind city will be known for the best DJs and musicians.
Conclusion: Some people are currently above average unproductive and unhappy (blind people apparently report higher levels of anxiety) members of society - not because they couldn’t do better or because they don’t want to, but because our system (build for and by seeing, hearing, generally healthy people) just doesn’t let them. If some of those groups had their own country - tailormade to their needs - they could not just gain financial independance and greater happiness. What is today considered a disadvantage probably comes with certain strengths. Some of those might help to enhance progress for humanity as a whole.