To be able to understand the dangers of Marxism, always an inevitably it must have a bloody outcome, we must understand it's core principles, and compare them to the core principles of the Christian Faith. The Judaeo Christian faith is based on the core principle of individuality.
The starting position of Communism is the complete opposite. Humans do not exist if they are dissociated from their class. Class struggle is based on the oppressors versus the oppressed. There is no ideal to strive for. The oppressed class is perfect in every aspect. With the oppressed class being perfect, the aim or higher good is replaced with annexation of the opposing class, which is the promised but never reached with the communist Utopia.