If you think condoms are no reliable, you can have a vasectomy, which is reversible.

As for your explanation about having children with men that they don't want to have as boyfriends, it not very believable. I mean, if they don't want them as a boyfriend, they won't want them as father of their children so they won't take the chance that the child has them as biological fathers so they can fill for custody and maybe even child support.

The woman who prefer to be mothers on their own would pay to a clinic because it is safer and there is no risk of a biological father coming latter filling for custody. Pay for sperm donor is cheaper than paying lawyers. The ones who plan to be single mothers would opt for the sperm bank.

What might happen is an unexpected pregnancy that they chose to keep. And at that point, either contraception failed (so no bad intention or fault on any part) or no part took care of contraception (in which case both parts were careless). So what you can do is not be careless yourself to avoid this scenario. And refuse to have sex with careless people.

But if you rely completely on others for contraception, you risk that they mess up or aren't as trustworthy as you thought.