Molu,
If there's something an admin wouldn't be doing if he knew he would be accountable for doing it, then he shouldn't be doing it anyway. If you are prepared to take an action only in the knowledge that you have nothing to lose if you are found to be wrong, then you are reasonably certain that you are in fact wrong in which case your actions are the most obvious abuse of power.
Define "accountable". Deleting a copyright violation is not an abuse of power, but I have seen users claim that it is (one particularly strident offender explained that, although he had not studied copyright, as a Law student he was allowed to declare direct copy and paste of entire articles from other sources as "fair use", and nobody could argue differently).
Administrators are accountable to each other, to ArbCom, to Jimbo, and to common sense. An administrator should not act inappropriately, and if he does, he should be held accountable. However, an administrator should not be afraid to perform a necessary but unpopular action. There is a very vocal, ignorant minority on Wikipedia in favour of just ignoring copyright law and stealing what they want ... this minority is easily powerful enough to sink someone's adminship out of sheer vindictiveness. Admins should be held to account for *inappropriate* actions, not *unpopular but necessary* ones. Your system makes no such distinction; it's pure madness to punish an admin for doing a good job --- and it deprives Wikipedia of an excellent volunteer.
Tenured professors don't provide a valid analogy in this case, Supreme Court justices are more likely and not all think appointing them for life is a good idea. Our justice system is far from perfect, there is no need to take it as model in Wikipedia.
Whose justice system?