I like to look at historical myths and Napoleonic legend is rich in these. One of them is that anyone who 'turned on Napoleon', or even criticised him, was of bad character and their opinions could therefore be ignored. From that it has followed that all their previous actions should be judged in that harshest possible light.
I have my reservations about the character of both Bernadotte and Marmont (Dupont was only guilty of a bad military decision at the worst) but they still deserve fair judgement. It is as incorrect to blacken their characters on account of their anti-Napoleon actions as it would be to glorify them on that account - which I'm not aware of anyone doing.
On the other hand, Talleyrand was as corrupt as they come and I don't think anyone has tried to absolve him but there is a good case for arguing that in 1814 he acted in the best interests of France.