Both are alternatives since this is not a dichotomy: a potential patient can opt-in before, opt-out before or they can leave the status unspecified until they a

Both are alternatives since this is not a dichotomy: a potential patient can opt-in before, opt-out before or they can leave the status unspecified until they arrive in the ER. Someone must make a decision for them and it will be either opt-in afterwards or opt-out afterwards. Since the group leaving the status unspecified is by far the largest, your practical ability to evaluate the procedure depends on what default is selected for the patients who haven't decided beforehand. Given the need, potential to save lives and widespread agreement among the public, I'd say there is no real ethical controversy here.