I would happily support the privilege of people to opt out of organ donations, as long as they are willing to irrevocably forego being the beneficiaries of an organ transplant.
Or hell, at that point, I'd happily make it opt-in.
Or hell, at that point, I'd happily make it opt-in.
It's fine to use donor status as a tie-breaker if multiple recipients are in contention.
EDIT: Plus the other reply about children.