The post-Hitler problem is nuclear weapons. Of course nobody would want groups like ISIS to get nuclear weapons. And nobody wants another religious dictatorship.
The bottom line, as bad as Hussein was, he was better than a group like ISIS being in control.
All we have done in Iraq is open the door to groups like ISIS to try to take power.
The only country within range of ISIS to have nuclear weaponry is Israel. The only country with nuclear weaponry that I think is very bad for them to have it is Pakistan. Again, ISIS doesn't measure up.
ISIS ain't Hitler. Hitler had a first world country, first world technology (by 1930s standards), a first world economy (even after it was destroyed by the Treaty of Versailles), a first world population, etc., etc. ISIS doesn't measure up. Hussein, Iran, ISIS, Qadaffi, none of them are Hitler.