Can a nation ever justify directly setting up dictatorships?
Ever? I guess. I can think of a few examples in Republican Rome alone where it made sense to do that, even if it was temporary, but it's definitely not the preferred option
They work well. See Cuba!
Are you talking about Baptista, the dictator that the US backed?
Yes, and if you didn't notice Castro was one too.
He sure as hell was never US backed, they almost went with a plan to murder their own citizens and frame him for it to get him out, although I should say Castro is a lighter ruler than Baptista was.
Well...they are efficient.
There's always an exception