Vladimir Lenin was highly critical of religion, saying in his book Religion:
Atheism is a natural and inseparable part of Marxism, of the theory and practice of scientific socialism.In The Attitude of the Workers’ Party to Religion, he wrote:
Religion is the opium of the people: this saying of Marx is the cornerstone of the entire ideology of Marxism about religion. All modern religions and churches, all and of every kind of religious organizations are always considered by Marxism as the organs of bourgeois reaction, used for the protection of the exploitation and the stupefaction of the working class.
Substitute “atheism” for “religion” in that last quote of Lenin’s and you will have the truth: atheism leads to the stupefaction of the working class — and ultimately to their murder.