When it comes to who we believe will be punished for their actions, we make exceptions all the time, gladly, for those whom we understand to be less than fully accountable for those actions – including their acceptance of Jesus and/or Heavenly Father in this life. We generally limit that type of exception to children and the mentally disabled, but I have no idea about any specific limitations Hitler might have had that might have limited his accountability – so, even in that case, I’ll leave the judgment to God.
(Psychopaths are a fascinating discussion when dealing with agency and accountability, since, by clinical definition translated into Mormon-speak, they are understood to be unable to feel the type of remorse that leads to repentance. Were Hitler, Dahmer, Bundy, etc. truly accountable? I certainly want to believe so, but I simply have no idea when it comes right down to it.)
I like the more complicated, multiple-glories concept of Mormonism specifically because it leans toward a break down of the tendency to categorize and judge others – to label them as either Heaven-bound or Hell-bound - to damn them in a real and practical way in our own minds. Sure, we still do it with three degrees of glory and Outer Darkness (and even degrees within the Celestial Kingdom), but the more gradations there are the less likely we are to be positive we understand someone well enough to make that call – or, at least, I hope that is the case.
If even for no other reason than that, I like the multiple degrees of glory far more than the heaven/hell split. I prefer a simple “many mansions theology”, and I like the idea of etermal progression that ends only when each person has reached his or her ultimate potential (whatever that is individually) – so I tend not to accept the idea that our final reward is determined when we leave this mortal existence. I see at least five stages of development built into our theology already – so, while I don’t believe in multiple mortal probations exactly, I certainly am open to the idea of more stages after mortal death about which we simply don’t have or need information at this time.