They don't need own children when they can just raise and indoctrinate other people's children. As long as they dominate culture, they will find enough kids they can indoctrinate through media, entertainment and "education". This plus the increasing percentage of immigrants and their kids, many of which will see nothing wrong with hating whites, as it doesn't concern them; on the contrary, they can feel like fighting nazis when beating up some white kid.

It's not enough to rely on leftists not procreating, they have to be removed from contact with children as much as possible.