With Palpatine Anakin was immediately aware that this was the Sith Lord that had brought so much crap down on everyone over the last 13 years. There was a definite threat, Palpatine had actually done bad stuff. I think you cannot compare him to a person, a boy, who was asleep and had not done anything yet.
I also know that if I walk around with a loaded gun that something might happen or it might be used, accidentally or premeditated. Taking the loaded gun out and holding it to someone's head for a second is not ok in my book even if momentary. Luke had the time to do that. He took the lightsaber off his belt and ignited it over his nephew's head. Way not cool.Also, you know there's a world of difference between a *momentary*, damn near reflexive thought that comes and goes in a second, and a premeditated attempted murder, right?