I see what you're saying, but it doesn't make sense until the child is actually born.

The issue with legislation like the one being proposed is that the woman has to go through every physical process of the pregnancy or termination, and legislation like this would probably lead to forced-hand abortions. You both created this kid, and there are generally laws around a dishonest pregnancy and child support for those edge cases where she pokes a hole in the condom.

What happens after the pregnancy is where things get tricky:

Congratulations! For better or worse you and your girlfriend have gotten pregnant and now you are deciding what to do. You don't want to keep it, she does, so she gets to keep it and you have to pay child support. That's the way it currently works, and probably the way it should stay.

But how is this fair? Why can't you just walk away if you don't want it? Well, it's because you both know the risks of having sex. It's pregnancy. And by engaging in intercourse you preemptively accept those risks, including having to help pay for said pregnancy once it is born.

So now we get to the issue at hand: if you don't want it and she does, why can't you just say "I don't want it, if you want to keep it fine, but I don't have to pay for it because I want to terminate it." Well, it's because you as the guy don't have to actually have the abortion. You don't have to undergo a DnC or take the pill that forces a miscarriage. The procedures for an abortion are extremely painful (especially the pill) and very, very invasive, and if you as the guy had the right to say "I don't have to pay for this because I don't want it" then there would be a lot of pressure for the girl to undergo a painful procedure she doesn't want to have, after you both accepted this risk by engaging in intercourse together.

The girls have to undergo the procedure, and by allowing you to back out of something you knew was a possibility when having sex with this person, you financially strand the person you got pregnant, and pressure them into going through the emotionally and physically painful process of having an abortion.

TL;DR: By having sex with someone you accept the possibility that there will be a pregnancy and that you will have to pay for it if it comes to fruition, but since you don't actually have to undergo any procedure to terminate it you don't have a choice in whether that happens.