I didn’t know that. The use of master-as-in-mastering doesn’t bother me. Nor does Master’s degree, mastering a skill, etc. But I can’t think of an ok context of slave. And when master is used in conjunction with slave, yeah, that’s not good.
ETA: “But I can’t think of an ok context of slave.” I don’t mean to kink shame. Unless you’re into that. 
