I didn't know that, but I'm not surprised! (I need to learn more about eugenics in Japan - my knowledge at the moment is really superficial.) After all, both socialism and eugenics tended to be utopian. It makes sense that people who were attracted to the one would find the other appealing, especially since there were so many strands of eugenics that engaged in some degree of class analysis, even if it did tend to be superficial and essentializing.

(Actually, one of the most interesting documents I've read and been unable to use this semester is a pamphlet book by a socialist, anti-racist eugencist, arguing against anti-miscegenation statutes on eugenic and socialist grounds.)