Hm. I can empathize with your perspective, as there's definitely an emotional connection which develops over the course of a pregnancy. But the child being "a part of the mother's soul", making surrogacy "worse than selling a kidney" is a highly subjective belief.

If we ban the sale of things that are "a part of [someone]'s soul", how do we adjudicate what is a legitimate part of someone's soul? For example, many people consider their creative works to be part of their souls, and I don't think anyone can objectively disprove this idea. If you invest years into anything, it will shape and affect you just as much as you affect it.