I am by no means an expert, but I find this topic very interesting. I appreciate everyone's posts - you all invariably bring up something I haven't considered and broaden my perspective.
Cons:
1) There are other methods available to address the donor/organ shortage. In some nations, citizens are automatically considered donors unless they actively choose to opt out, for example. The opt-in structure of the donor system in the U.S. facilitates the passive perpetuation of the problem.
2) Compensating donors creates incentive for donors to put their own health at risk (when their health may already be compromised due to poverty, malnutrition, etc), and an incentive for donors who need money to lie. There are regulations in place in some plasma centers to prevent people who are homeless from donating, but in my (arguably young and limited) experience, I would never underestimate human resourcefulness.
3) Healthcare is already expensive, and paid donation could open the door to increased stratification of healthcare for the wealthy - only those who could afford to pay a donor might receive marrow.
Pros:
1) Women can already be paid for egg donation, and eggs are not replenishable. Bone marrow is replenishable. My understanding is that the risks of bone marrow donation were more comparable to that of donating a kidney, and this is why it was covered under NOTA. As medicine has improved since 1984, the risks have greatly decreased for bone marrow donation today, and the risks now are more like donating plasma.
2) In 2011, the 9th Circuit Court of Appeals ruled that it was legal to pay bone marrow donors. This only applies to the states under the 9th Circuit, but does set a precedent.
3) Ethical concerns about creating a direct market for bone marrow seem not to take into account the low probability of finding a genetic match - this would not be a great way to make money. Concerns about creating a market for general human tissue could be ameliorated by compensating donors with vouchers that can be used for medical expenses, housing, food, education, etc., rather than simply paying donors cash money (I think this is actually how it's done with marrow in the states where it is legal).
4) There is a real concern that people desperate for money would be put at risk by a program allowing organs to be sold for money. However, these people are already at risk due to the thriving black market as
@jd989898 pointed out. The creation of a legal, regulated market would likely actually increase protection for those who currently feel compelled to sell their organs.
5) Financial compensation does increase donation and supply (just look at the plasma center model, where paid U.S. donors supply about 70% of worldwide plasma).