How effective was terror in controlling the people of the USSR in the period 1929 to 1941?

Stalin, the "Man of Steel" is known for his use of terror during his legendary rule. He was the kind of leader that would stop at almost nothing to accomplish his goals. "Stalin is a Genghis Kahn, an unscrupulous intriguer, who sacrifices everything else to the preservation of power....He changes his theories to whom he needs to get rid of". Through his 5 year plans, Stalin introduced Collectivisation into the rural parts of Russia to …

…terror and used the NKVD to carry out horrendous atrocities in the attempt to rid himself of all his 'enemies'. Stalin embarked on a series of purges on the party, army and society which horrified the world. I'm sure that Stalin, at the time, thought that he did what he did with the best intentions. However, it can be said that some of worst things imaginable have occurred when people act with 'the best intentions'.