Unsubstantiated claim. He is used as a negative advertisement of Soviet era.
If you read carefull the trial in Nuernberg, Germany was not punished at all and they were worse.
For me he showd disrespect for his comrades. The battle of Kursk had much more casualties that it needed to be. The same happens for the war in total. He was completely incapable to be a leader. Useless and he did not care for his country. He also demonized communism and was in reality a dictator that pulled the right strings to become leader of a party (exactly what happens with leaders usually). He was also a racist and mass exterminated people. If he was different may the bloodshed of WWII would be prevented.
But the same was Pinochet and the western media covered all his crimes.
"For example, there is a tradition in many newsgroups and other Internet discussion forums that, when a Hitler comparison is made, the thread is finished and whoever made the comparison loses whatever debate is in progress.[8] This principle is itself frequently referred to as Godwin's law."
I'm not sure what you mean by this, the crimes of Stalin are probably over exposed in Western media, if anything. There's no shortage of people eager to inform you that Stalin killed people, even if it's completely off topic!