In the interest of disclosure, I don't have a choking kink - but I've also been on the internet for nearly three decades at this point so who even knows anymore.

My understanding is that a large part of it is trust. The chokee is quite literally putting their life in someone else's hands and saying, "I trust you enough to do this without killing me." Of course, throw it into casual relationships and it kind of muddies that a little bit - after all, how can you trust someone you just met at a bar/on Tinder/etc. enough to know that they won't kill you? But I think that's where it starts, anyway.