Legal Question in Constitutional Law in Colorado

Because men aren't the ones who get pregnant.

You presume that men's and women's roles in having a child (which is different from raising one) are equivalent, but they aren't. The man's role is over as soon as they are done having sex, but the woman's is just beginning. The pregnancy affects her body in fundamental ways for nine months but has no effect at all on his.

One of the main reasons we allow abortion in this country is that we give people control over their own bodies. If the law worked the way you propose, then control of women's bodies would often belong to men.

Don't forget that the identity of an unborn baby's father can be hard for third parties to know. Should any man who claims to be the father be able to prevent an abortion? There are plenty of zealots who would hang around abortion clinics to make precisely that claim every time a woman walked up to the door if it would prevent her from aborting her pregnancy.

You ask "How can one party be forced into decades of obligation because of someone else's decision?" But if abortion was legal only when both parents approve, then a father who wants the child could force the mother into "into decades of obligation".

Or does being forced into such obligation only bother you when it happens to a man?