For some reason, we believe the Myth of a Better Alternative. We believe that, if someone or something is bad, there must be a Better Alternative. We see an evil despot overseas and believe that if he were overthrown, the Better Alternative - democracy and freedom - would flower.
The problem is, of course, we don't know who will rise to power after a bad dictator is disposed. Will the new government be better? Hopefully, but it could easily be worse. We just don't know. We can't know. Removing a dictator could result in a long, bloody civil war that kills thousands of people and literally destroys the country, only to be followed by a more evil dictator.
Czar Nicholas was not the best ruler, but I think many Russians - the 20 million killed by Stalin come to mind - would have preferred the Czar to the communists.
The United States does not need to intervene everywhere in the world that has what we consider a less than optimal government. We just can't afford it. Besides, we don't know what's best for other countries. Why don't we just save thousands of our soldier's lives, trillions of dollars and let the rest of the world work out their own problems?