Religion is an ideological weapon to justify the suffering of the poor
Misleads the poor into believing their suffering is virtuous and they will be rewarded in the afterlife
Creates a false consciousness
Lenin
Described religion as a 'spiritual gin'
An intoxicant doled out to the masses by the RC to confuse them and keep them in their place
Creates a 'mystical fog'
Alienation
Capitalism causes alienation
Workers are alienated because they don't own what they produce and have no control over the production process
In the dehumanising conditions of the WC they turn to religion for consolation
Acts as an opiate to dull the pain of exploitation
Promise of afterlife distracts from the misery and true source of suffering
Evaluation
Marx shows how religion may be a tool of oppression but ignores positive functions
Some Marxists, eg Althusser, reject the concept of alienation as unscientific and so this would make the concept an inadequate basis for a theory of religion
Religion may not function effectively as an ideology - EG pre-capitalist society where Christianity was a major element of RC ideology it had limited impact on peasantry