If a single mother is on welfare here in the US, then she would be legally required to go after the father of her child, whether alpha or beta, for child support. And she can already voluntarily do that in any case.
Vasectomies can and sometimes do fail. Heck, even bilateral epididymectomies can fail! As for trans women, I am only attracted to ovulating women. Seriously. Sorry.
How is that in any way unfair? Children (and child support) are one of the risks that we take on when we have sex. We take calculated risks with each and every decision we make during our lifetimes. Then you shouldn't complain about anti-abortion people using that very same logic, eh?
Did you read the court case? Yes. Generally the only way someone can take over legal responsibility for child support is if they adopt the child. And child support insurance? Because there's a technical difference between indemnification and assuming legal responsibility.
Also, what about a parent promising to pay someone else's share of child support for a child who is not related to them and whom they are not legally responsible for?