Communisim is dangerous why? Because it spoke to the largets and most disillusioned class in Europe?

I think you conflate authoritarianism with communism. The Bolsheviks just replaced the Romanovs at the top of the Russian hierarchy. Calling your country communist doesn't make it communist any more than the Democratic Republic of North Korea is democratic, or a republic. The USSR was dangerous when a sociopath like Stalin was leading it. Communism, not really.

That being said, the USSR raised many more millions out of poverty in a shorter period of time than the capitalist US. The only country to raise more people out of poverty more quickly than the USSR? Communist China.

Capitalism has done great things, but also horrible things. For example, all those war dead from WWI were from wars started by capitalists, not communists. WWII? Also not started by the communists. US multinationals - particularly Ford and GM - supported the Nazis throughout WWII.