Getting rid of Mugabe

Mugabe is making noises about stepping down if he gets immunity. Norm Geras points out part of the ugly trade-off:

the demands of justice for crimes of the magnitude of Mugabe’s are not to be lightly dismissed; at the same time the people of Zimbabwe desperately need peace and time to repair the damage his regime has done.
Norm thinks he has found a way to ease the problem.
It may be worth pointing out, however, that an agreement to offer him immunity from prosecution doesn’t bind anyone who isn’t party to it. If Mugabe has committed crimes against humanity, then he can be brought before the courts of any country, for these are crimes for which there is universal jurisdiction. And that may, indeed, be an argument to add to the others that there are in favour of the Zimbabwean opposition offering such an agreement.
Sadly, I think Norm is wrong here. There are two difficulties here. First, Mugabe is not a fool. Imagine a policeman trying to get a suspect to cooperate by promising not to arrest him, but then adds, “of course, the policeman next to me might still arrest you.” It sort of defeats the purpose of the deal, and Mugabe would be a fool to take it, and Mugabe is not a fool. Second, Norm is leaving out important parts of the trade-off. It is not just Mugabe, but future Mugabes. If future Mugabes think that they can destroy a country and get off easily, there will be more of them.