Steve Jobs Urges Californians to Become Organ Donors
businessweek.com
businessweek.com
People use the default choice most of the time since they believe it is default for a reason and don't think about it.
Why does everyone involved in the organ donation make money (surgeon taking out organ, surgeon transplanting organ, etc.) except the supplier of the raw materials (donor)?
Murder (and other initiations of force) is both immoral and illegal, so there's no conflict there - you need your organs to live, so these laws (and many others) already criminalize the theft of organs.
There's no valid reason that you or your estate shouldn't be allowed freely sell things you don't need anymore, including your liver.