I guess dissenting Chinese and Tibetans don't count

Former President Jimmy Carter explains why he would not support a boycott of the Beijing Olympics:

As president, Carter led the boycott of the Moscow Olympics in protest against the Soviet invasion of Afghanistan. "That was a totally different experience in 1980, when the Soviet Union had brutally invaded and killed thousands and thousands of people," he said, rejecting the idea of boycotting the Beijing games to protest China's crackdown in Tibet. He did not address whether just the opening ceremonies should be boycotted.

So you see, because the Communists don't have to invade to continue to be repressive towards their own people and the Tibetans, not too mention other Asian ethnic minorities within their borders, it doesn't really count.