I've read so many history books that all give different estimates of how many people he killed in his purges - estimates between 2 and 7 million. Some people say that it was excusable because the industry he developed by urbanizing Russia and forcing work in the Gulags allowed the Soviet army to be prepared enough to fight off Hitler, and provide a framework for a strong economy. His constitution also set the same basic rights as we had in America at that time, and sometimes even more (expecially for women).
(Just a little tidbit to see if anyone will take a pro-Stalinist side)