Conversation so far:
Was Havelock Ellis for or against sterilization?
Havelock Ellis was strongly opposed to the idea of castration for eugenic purposes.
Did Havelock Ellis have another motion in mind besides castration for eugenic purposes?
Ellis was witness to the rise of vasectomies and ligatures of the Fallopian tubes, which performed the same sterilization without removing the whole organ. In these cases, Ellis was favourable.

Question: Why did he believe that?
Self-contained rewrite: Why did Havelock Ellis believe vasectomies and ligatures of the fallopian tubes more favourable for sterilization?