Can the assasination of a dictator be justified?

Consider the obvious: Hitler.

Absolutely.

Justice is not the same as law.

regardless of who thinks it is wrong somebody will think it's right

be very careful in how you think

if you can justify killing a foreign dictator then countries can use your logic

to justify killing the head of your government which is probably not what you intended

It's far simpler and a lot less messy just to hit the "No" vote button.