I think any reasonable mourning period has long passed for Hitler, Stalin, et al. However attacking recently deceased immediately after their death is just not cool. Regardless of what you think of them, assholes have families too. Let them grieve in peace.
Any person that is mourning the death of this people as of this moment are either trolling or they are Nazi sympathizers for Hitler and Genocide Lover for Stalin. I do agree with you about respecting the dead, the loved ones of the persons responsible for a horrendous crime is to be respected unless they participated in it.