>>724903028 (OP)
>Ignoring the fact that nobodies actually do have hearts
No, you got it the wrong, Nobodies do are "born" without a heart, the thing is that they can naturally "grown one" which matures with experiences and about your second question, getting hearts though KH was a big lie, instead they would have gotten copies of xenahort's heart and become his clones which was his plan all along.
