"who gets to decide?"
I would suppose the legal framework of whatever country you live in. But that's a very imperfect solution. It's what decides the law that we all live under and should be created under democratic principles. But that's a big should. A very big one.
It would boil down to one of two things - 1. The law decides what is allowed, or 2. We all do what we like. 1 is far from perfect but it's the best we have right now.