I think the premise of your questions is flawed. You seem to be presuming that threats and/or violence are always wrong. Circumstances can create the aforementioned "shades of grey". Just as a police officer shooting an armed robber is not the same as the armed robber shooting his victims, so is forcefully opposing a brutal dictator not the same as becoming one. It can be better to forcefully oppose evil than it is to appease and, therefore, enable it. Or do you lament that the world is not ruled by Nazis now?
I've actually wandered many times about how much "evil" is required to counteract evil. The short story is, that there is no easy answer. Personally, I'm leaning on exploring all viable alternatives, to the point of leniancy. Each one of us, has to draw the line between, overeacting to a perceived threat and the just being passive. However, the higher the "stakes" (i.e. population envolved) the more cautious one must be to the use of violence.
And since we're giving examples, let me ask you this? How comparable is the police officer and robber example, to the one where a country proposes to put an end to another country's nuclear program, by drawing plans that focus around the use of tactical nukes?