It helps if you look at it from the perspective of the capitalist class. Workers are a form of free capital. Capitalists don't have to assume any of the burdens involved in creating life, raising a child, acculturating them to social standards that make them suitable workers, etc. They don't even have to pay for the education or training that makes them capable as human capital in various industrial contexts.

All those costs are dumped onto the working classes, not just as parents (usually the woman) who are expected to deliver a baby, nurse the baby, raise the resulting child until they are the age of the majority all without any wages, access to benefits like retirement plans or health insurance, etc. but also onto taxpayers who subsidize the rest of the costs outside of the home such as their schooling and transportation to the schools.

There is a huge leverage here that the working class does not take by organizing the production of themselves. If we all agreed to not have children and demanded fair compensation for any new production of human capital, society would be much more just and the capitalist class would have less room to exploit us.