I agree with the first one. Everyone should be able to love any adult in any way shape or form they want with consent of all involved parties.

But the the relatives one runs into issues with abuse and clear voluntary consent. Grooming is an actual thing, and a much bigger potential risk if the groomer is raising you from your infancy. I would add the caveat if you really want to make it acceptable, it should only be allowed between people of the same generation, and only when they're well into adulthood.

It’s legal in many countries. You might want to check out how it plays out there in terms of human rights?