The Sotomayor dissent was awful. It's an absurd argument with no real basis in reality. Whether the president is immune from ordering the assassination of a rival is largely irrelevant, because it wouldn't get to a criminal trial anyway. It's already illegal for the seals to carry out that order as well.
The president told me to do it isn't a valid defense
That's a fair comparison. Superman is powerful enough to always make the right choice, even when it's hard. The appeal comes from Superman discovering and making the right choice.
Batman makes the necessary choice (apart from killing), which isn't always the right choice. The appeal comes from stories where Batman walks the line between criminal vigilante and hero who saves the day.
Banks would go out of business and credit unions would look a lot more like banks. This is assuming both business and personal accounts move. If just personal accounts move, not much happens.