> so why do all open source licences necessitate that I allow my work to be put to evil uses as well as good?
Most likely because defining good and evil is very, very hard, and you don't want vague language in licences. "Not to be used by evil people" doesn't work, because all it takes is to say "I'm not evil, thanks".
Saying "no military use" etc will also just open up a rabbit hole of what exactly is military use, and you don't want to have a lot of court cases, and you also don't want uncertainty, e.g. somebody building a SaaS product that then has to vet all customers whether they may have military contracts, even if it's only for catering at some event.
Most likely because defining good and evil is very, very hard, and you don't want vague language in licences. "Not to be used by evil people" doesn't work, because all it takes is to say "I'm not evil, thanks".
Saying "no military use" etc will also just open up a rabbit hole of what exactly is military use, and you don't want to have a lot of court cases, and you also don't want uncertainty, e.g. somebody building a SaaS product that then has to vet all customers whether they may have military contracts, even if it's only for catering at some event.