If you look at any economic exchange there is the potential for robbery and ‘non-consensual trade’ as you put it.
We have factories, and we also have sweat shops where immigrants or kids are forced to work for nothing.
Your argument could be applied to literally anything.
So, build a fence on the southern border.
I'm not aware of true slavery in the sweatshops in the USA, but certainly some pay less than minimum wage.
Are you folks willing to live with a little slavery to get a bit of longer life? How much are you willing to tolerate?
One thing about sweatshops, when you do find them and shut them down, the victims are still alive.
And with the sex trade in England, it looks like a fair percentage of the workers are coerced. You can't say that about the general work force.
I’ll bet the solution to this is quite simple and cheap.
If one agrees to organ donation with one’s drivers license, wave the license fee, or maybe even pay a nominal amount. The actuarial odds that one would actually become an organ donor is commensurate with such a remuneration. The state would be reimbursed by the hospitals for donor licenses issued, not organs actually harvested. The actual rebate amount would be determined by what a statewide hospital pool was willing to pay in the aggregate. It would be like insurance in reverse and not incentivize any Frankenstein scenarios.
All potential donors benefit, the hospitals and recipients benefit and the state would be entitled to a percentage, say 10% or 20% of the hospital pool payments.