It depends on what you mean by communists, leaders, and crime against humanity. All those are vague politically loaded terms.
Communists are just label. I can think of a few communists leader that are “fine”. I called them fine because they help their countries out of communism. So in a sense they’re communist leader. In a sense they’re not. These people does not commit any crime against large number of humans.
The issue is not christianity. The issue is the very human nature that’s hidden. In other word, in the absent of christianity, such as in china, in muslim world, and among liberal feminazis, we too will see opposition to prostitution or any efficient system.
The real issue is human nature. We can think of marriage as prostitution where everyone is the pimp. Everyone wants to be pimp and they do not want to compete with more efficient pimps. That’s all.
Namely, genocide against those who don’t feel like getting married.
Imagine of some countries prohibit commies/non commies, or any specific group of people as unfit to reproduce. Then we would consider that a genocide.
Imagine if that country start stoning commies/non commies, christian/non christian, muslims/non muslims, for reproducing (or attempting reproducing 
). Then it would be genocide.
Even if members of those oppressed group can simply switch, they may not feel like switching.
What about those that don’t feel like getting married?
In some countries, for example, kids born out of wedlock do not get birth certificate. If this is not extermination of unmarried people then what?