I know there are other objections as well, in both cases. People fear the exploitation of the vulnerable, for instance. But if that’s the concern, it is tragically misplaced. Illegality does not make demand disappear; it just drives it underground, and people are far more likely to be taken advantage of in a black market than in a legal one.
Sex can be an expression of love, but for someone who is starved for physical contact, sex without love can be a lot better than nothing. As for someone who is in pain, whose daily routine revolves around the need for regular dialysis, whose very continued existence is in dire peril, a kidney without love will save his or her life just as surely as one that is donated. And it will likely do so a whole lot sooner.