At least Kai thinks of himself as human, which he is well aware helps not at all when he looks like he does. When he's done he drops the collar to the ground and kicks it away with a look of disgust on his pretty face. He definitely would have done that for anyone, and he's assuming that Paris sticking around means he thinks he might need more protection.

"It's incompatible with magic." Only thing that can kill the elfin at least.