I've seen all kinds of justifications for it. I saw one of the more highly suspicious furries claiming that they have to use Signal because so many furries are disabled that they can't figure out how to use anything more complicated (which other options really aren't, they just insist on comparing it with Matrix which is god-awful and everyone comments on being viscerally disgusted by). People don't really need anything more fancy than iMessage. You're being babies. Just use your public borked and corrupt messengers and mentally sort them into the Facebook pile. If it's not secure from federal law enforcement, then it's not safe to have conversations on freely, since class consciousness, common sense, and human rights are illegal.