A communist can be religious. In fact, they usually are!
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
Sean the communist was trying to convert a few people at his workplace to communism. One guy objected to the idea, and that guy was subsequently fired.