I am paraphrasing information from Wikipedia here: Some thought this was a political trap, to encourage dissidents to step forward only to be ensnared. But it seems that Mao actually thought people would respond with positive critiques to iron out wrinkles in the system, perhaps complaints of petty corruption or local ineptitude. After an initial luke warm response, he basically then said, 'no really, what do you really think? But you know, be healthy about it.' Well then the response was overwhelming in damnation of the system, the party, the major elements of communist rule.
It's still not clear whether it was all a trap or if Mao truly was trying to know the opinion of the people, but he shut it down in 1957. The end result was the persecution of intellectuals, officials, students and dissidents, with over 550,000 people humiliated, imprisoned, demoted or fired from their positions, sent to labor camps, tortured, or killed.
This, then, is what Kelly was referring to in 1966, as China launched the Great Proletarian Cultural Revolution in August of that year.