You probably haven't been paying attention, but the US Gov't make dissidents disappear all the time. They just do it with a velvet glove on, whereas we're more accustomed to complaining about/being distracted by the heavier hand represented by the propaganda against North Korea.
The US gov't is not as innocent as you might think when it comes to handling dissidents. Its just very, very good at maintaining the facade that its all done 'for the greater good of the people of the United States and its possessors'. The USA is, after all, a PR-first nation.