These regimes frequently use Islam to legitimize their own political actions, and thus set the stage for another kind of Islam in opposition to them.
It is not an accident that nearly all the hijackers were from countries we consider our allies, but we are busy bombing and attacking a non-allied country which merely made the mistake of allowing them to pass through its territory, and then thumbed its nose at us.
If we were to support regimes which have "liberty and justice for all" as their goal we would not have to try to determine who is a good dictator and who is a bad one.