The US leaves repressive totalitarian governments alone untill they start messing with other countries and violating the soveriegn rights of other nations.
The US supports repressive totalitarian governments so long as there is money to made, period. Any time a government--any government--interferes with this, efforts are made to "correct" it. This could mean diplomatic or economic coercion--or straight military intervention, in cases where a pretext can be employed to support it. "Democracy" does not enter into the equation, except as a an obstacle to be avoided, since ordinary people in large numbers have shown a historic incapacity to put the needs of private enterprise ahead of their own. In this respect, strong-arm dictators are much easier to enter into "constructive" dialogue with than any diffuse population.
You do not understand why we try to impose Democracy on others untill you live in one of these totalitarian countries. When your door gets kicked down in the middle of the night you really apprieciate freedom.
In that case why not "impose democracy" in China instead of celebrating their lack of basic freedom as an "opportunity" to make money? Contrary to popular mythology, "democracy" is not the inevitable result of economic growth. For reasons that should not be hard to discern, Western elites like to believe that as their profit margins increase under any given circumstance, so does the general wonderfulness of life on planet earth for everyone else. Since they own the media, this is the message that they choose to repeat again and again for our benefit.
The American business community does not care about "democracy"--after all, they are the ones who own the country, fund political campaigns, staff the executive, and in other ways preclude it here at home. They care about making money. So long as Hussein, Noriega, and other tyrants help us make money, they are our good friends. As soon as they become the least bit disobedient or disruptive to our interests, they are replaced. This is history of American foreign policy in a nutshell--easily verifiable should anyone bother looking at the (not secret) documentary record.