What would be the consequences if we did allow Presidents to be prosecuted and some of them did spend the rest of the life fighting prosecutions?
It seems to me the consequence would be that we would have Presidents who act carefully to not break the law. Are there any other consequences?
I've heard it said that "democracies are where the people in power lose". We've all seen "democracies" where the party in power never loses; those aren't real democracies. Likewise, I would say nations that are truly governed by law are where those in power face legal prosecution.
(Also, what's so bad about prosecution? If a person is innocent, the legal system will find them to be innocent, right?... Right?)