[vidarh]

The more extreme example of the benefit of allowing criticism was Mao's Hundred Flowers campaign, where the government actively encouraged criticism, only to abruptly change course, and arrest many of those who took the opportunity.

In other words: Encourage a little bit of criticism, and you will be able to observe those who join in - even if they don't go too far - and be able to obtain a handy register of people to pay extra close attention to.