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@Bones
I'm not justifying a difference based on location. The differences are multifaceted: the mother has made a commitment to have the child, has gone through with the pregnancy, and is currently raising the child, which includes the financial burdens involved. You talked about how paying child support is a form of enslavement, but that resembles the commitment that a mother makes to their child. The father is being held to the same commitment. You could argue that this is solely an issue of consent and that all that matters is who got to consent to what, but that's reductive. Issues of consent are a subset of the issues involved, not their entirety.
In general, though, the argument you're making seems to be that being compelled to pay is functionally the same as the burdens placed on the mother. I personally wouldn't consider what a mother goes through in order to give birth equivalent to financial payments, but hey, what do I know?