"I got an idea, go back in time and kill Osama's mom" is the quote you wonder about why it was deleted. Because it's a downright death threat towards Osama bin Laden's mother. That's why. At least that must be what the moderator in question must have had in mind. Since the moderator in question was not me, it's always guessing work, as I cannot look into other people's heads.
Loads of communities ban the practice of death threats even as a joke (sometimes with the exception when the threatened person is a fictional person).
Now a few things should always be kept in mind:
- Threatening a terrorist with death is still a death threat, regardless what that terrorist has done.
- Threatening a relative who is (as far as we know) not involved in the crimes is not any better.
- "No one has a time machine" is not a valid excuse. The wish for somebody to die has been pronounced, and that is where the borderline is still crossed.
- Now the comparing to Hitler doesn't work here. Hitler has been dead for decades. As far as I can check Bin Laden's mother is still alive (there is nothing I can find stating otherwise).
- Also note that Bin Laden still has great support, even in death, and that your post can be used against the West in their propaganda. Even though there are still nazist people, posts about killing Hitler will at the current state of things not likely cause that effect. Comparing things is always a dangerous thing to do. Also it's possible the moderator in question didn't see thing. Comparing cases is always a dangerous thing to do.
Now I am just trying to get a full picture of what the moderator was thinking, as I am not in the position to say if this moderator was right or wrong or if I would have done the same thing if it were me in their position. What I do know is that this meme doesn't impress me.