They believe that a society in which assets are state owned is practicle, and would actually work out and help the residents of a country.
Well, most of them believe that. Some believe that it's a way for them to gain power.
And really, that's all Communism is about. Power.
But communists will continue to go about trying to achieve something which would only be socially devistating. And they'll do whatever they can to try and achieve it, hurting anyone who comes in their way. See: End justifies the means.
The concept of communism, just like the concept of democracy, would work fine if it was not corrupt, or if it did what it claimed is stood for.