A New York assemblyman wants NY to adopt a presumed consent law for organ donation. 

The legislation, introduced by Assemblyman Richard Brodsky, a Westchester Democrat, is in two parts: the first step would end the right of the next of kin to challenge the decisions of their dead or dying relatives to donate their organs.

In a second measure, which is far more contentious, people would have to indicate in official documents – their driver’s licenses, most commonly – that they specifically don’t want to donate organs. If the box is not checked, it is presumed the person wants to donate.

The first thing to note about this proposal is that contrary to what Brodsky suggests, the problem isn't families who refuse to follow the wishes of the potential donor–as a rule, families who know, follow.  The problem is that families often don't know what their loves ones would have wanted because many people don't sign their organ donor cards.  

In fact, the way presumed consent actually works is not by overriding the wishes of the family it's by making the wishes of the potential donor more clearly known to her family.  In most presumed consent countries the family still has the ultimate say in practice because what doctor is going to want to go against the wishes of the family in a time of grief?  Instead, presumed consent increases the probability that families say yes by changing their background information from my loved one didn't opt-in to my loved one didn't opt-out. 

So under presumed consent we get more families saying yes–but not all–and there are other constraints such as the number of people who die in a way that makes their organs available for transplant and the availability of transplant surgeons and facilities to do the operation and so forth.

In a roundtable on this issue with Sally Satel, Art Kaplan and others, Kieran Hiely notes:

Spain’s success is due to effective management of the transplant
system, not a simple legal rule. Similarly, Italy’s donation rate grew
rapidly in the 1990s thanks to investment in its system, not because of
its long-standing presumed consent law. Some countries, notably
Austria, do have “true” presumed consent, with no kin veto. But they do
not outperform countries like the U.S. by any great margin.

I'm actually a bit more positive than Kieran, the best evidence is that presumed consent raises donation rates by perhaps 20-30%.  Not bad, but not enough to eliminate the shortage.  To do that, as Satel notes in her contribution to the roundtable it will take live donation.

Kieran also writes:

It’s also worth remembering that, since the 1970s, the U.S.
“transplant community” has worked hard to allay public concerns that
surgeons might be too eager to harvest organs, or that the state might
play too calculating a role in deciding what happens to the bodies of
potential donors.

The latter point is especially important in the United States.  Brazil, for example, switched to presumed consent and then switched back to opt-in when people became fearful and outraged and donation rates fell.  It's not hard to imagine similar blowback in the United States.

It's also worth remembering that considered as a whole the U.S. system is the best in the world.  Spain does have a very high rate of deceased donation, but it does poorly on live donation.  Iran leads the world on live donation because it compensates donors but due to religious feelings about the sacredness of the body Iran, like other Muslim countries, does poorly on deceased donation.  The US does well on both deceased and live donation and in total leads the world.

We can do better but we do need to tread carefully.