Why the communists’ approach to morality, that is “the end justify the means”, resulted in the death of millions in the 20th century?

The idea behind it was that there should be a dictatorship of the proletariat, that is, the dictatorship of the working class who make the majority of the population. It was believed that this type of a rule would ensure that everyone was satisfied and equal in all aspects. Those who opposed any of the policies were seen as fighting against the people and against the group identity and against equality, so they would be killed. This fact that you could easily be described as the enemy of the people resulted in numerous political opponents being killed.