Why did Khrushchev criticize Stalin's rule?

He wanted to tarnish Stalin's image as a leader and the myths that surrounded him, and detach the 'Stalin Cult.' In doing so, he would not be criticised of being the culprit of the large amount of people that were still in camps, as on their release they would expose the truth of the repressions. In addition to this, by disregarding his role in the purges, he accused the other senior party members, and stated they were more responsible for the crimes committed. Following this further, the speech gave him the opportunity to begin the process of de-Stalinisation, granting him the chance to turn against Stalin's policies with less criticism from Soviet citizens. Also, Khrushchev believed that Stalin's system held further progress to which he could take up the initiative to produce and reform to his creativity of the policies.