Molotov–Ribbentrop Pact was similar to pacts that every other European country had - including Poland[1]. Except that Poland had it since 1934 and USSR only since 1939. Stalin made it after realizing that Britain and France were playing him from April to August 1939 [2].
[1] http://en.wikipedia.org/wiki/German%E2%80%93Polish_Non-Aggre...
http://en.wikipedia.org/wiki/Munich_Agreement
"The agreement was signed by Germany, France, the United Kingdom, and Italy."
and:
http://en.wikipedia.org/wiki/Tripartite_Pact
Initially: "Germany, Italy and Japan"
then:
"Hungary (20 November 1940), Romania (23 November 1940), Bulgaria (1 March 1941) and Yugoslavia (25 March 1941), as well as by the German client state of Slovakia (24 November 1940). Yugoslavia's adherence provoked a coup d'état in Belgrade, and Italy and Germany responded by invading Yugoslavia"
Note that some countries first signed and only then the Nazi regimes came to power in them. Hard time in Europe then.
It's just a part of massive denigration campaign.
Stalin was a mass murderer:
"The exact number of deaths caused by Stalin's regime is a subject of debate, but it is widely agreed upon that it is on the order of millions."