4 major parts of the theory of blameworthiness.
Uncertainty
Difficulty
Involvement
Seriousness
I could easily argue for two of those in Hitler's favor possibly the other two with a bit of a stretch.
The involvement is the easiest part to argue for Hitler holding little blame or at least him having blame equal to that of everyone involved in the Nazi movement. In accordance with the theory, if a person is part of a group that performs a "wrongful" action, the blameworthiness is mitigated. On the other hand, some people believe that instead of mitigation, the blame is equal on everyone's shoulders, regardless of their part in the deed.
Difficulty concerns the.. difficulty of doing what is "right". After he had gotten the ball rolling, even if it was not his original intentions, Hitler would have been under considerable duress and pressure from his party if he had suddenly decided to take a different route. Again, this would mitigate his blameworthiness.
Now for the stretch...
Concerning seriousness. This part of the theory basically says a person holds less blame the less serious their offending actions are. ex. Killing someone creates more blame than stealing 10$ from a wealthy person. Now, I do not necessarily agree with what I am about to argue, but, using this theory as a platform, an argument can be made. The seriousness defines actions as minor and major, but provides no reference scale. In the grand scheme of the entire lifespan of the world/universe, the holocaust could easily be seen as a minor event. The extinction of the human race would likewise be considered minor if the scale were large enough.
The final stretch to be made is that of Uncertainty. "If a person is uncertain whether an action is wrong because the facts are unclear or because the question of the relationship between the facts and the relevant ethical standard is unclear, that person's blameworthiness is mitigated." Relevant ethical standard varies from person to person, whether it be based on religion or worldview or something else. If a majority reaches a consensus, that does not mean the majority is correct. However, being correct in itself, becomes irrelevant in the face of a majority. That is simply how our current societies function. If you subscribe to a higher believe, that there is a universal right or wrong, then it is not that much of a leap in faith to imagine a higher power in which Hitler's actions were considered to be right. If you do not believe in such a system and instead believe that actions are to be evaluated on your own set of standards, then you can likewise understand that someone else's standards could be such that killing people is fine if it achieves a greater goal. Many institutions already hold this belief. Military, religion, government, individual people. I would wager that almost anyone can think of a situation where they thought killing someone would be justified. How about traveling back in time to kill Hitler in an attempt to stop the holocaust? Hitler was acting for his own reasons, but also for his vision of an improved Germany. What he did is considered by many to be wrong, but the ends to his means was to be a stronger, superior German nation.