The tricky thing about organ donation is that the default choice tends to be 'postpone deciding'. For society at large this is harmful. Hypothetically, if you could ask someone's ghost after they've died on the hospital table, I bet most people would gladly donate their organs (perhaps with the occasional “Oh but can you please leave my face untouched?” thrown in) after accepting their untimely demise. But we can't. So with opt-in and a with a mandated binary choice at a set time you go for the safe option, which is 'non-donor' (“I'll change it after I've thought it through.”).
Hypothetically, if you could ask someone's ghost [...]
I bet most people would gladly donate their organs
Don't you think it's a bit of a stretch to imagine you know someone's preferences better than they do when they've explicitly stated their preferences through a forced choice mechanism?But at that point, they have made a choice (as ill-informed as it may be) as opposed to one being made for them.
I'm an organ donor. I encourage others to do the same. That said, when a government makes choices about your body for you -- even if the choice seems "right" -- I find it a bit unsettling.
Freedom is measured best when the "wrong" option is chosen. It also illuminates those who just give such freedom lip service.
FWIW, Richard Thaler, who played a big role in creating the field of behavioral economics, has argued in favor of "mandated choice" for organ donations at the time people renew their drivers license [1]. His concern with default opt-in, as I recall from one of his books, is that defaults are so powerful that they may not really create implied consent.
[1]http://www.nytimes.com/2009/09/27/business/economy/27view.ht...