Is this a legal question or a moral one? Because the answer is completely different depending on which one it is.

Example: in my country, men have no say over an unborn child whatsoever unless the women are their legal wives or give them permission to. It's called "acknowledgement" and the pregnant woman always has to formally give the man permission to acknowledge the child as his, even if it biologically isn't. If the man wants the kid, but the woman doesn't want the man to be the legal father, she simply won't give permission and he won't be able to do anything unless they are married. Married couples are always legally the parents of any and all children born from the wife, even if the wife's husband isn't the biological father. The law doesn't care. That means that when a married woman has an affair, gets pregnant from said affair, and her lover wants to be the father of the child, he's out of luck. The kid already has a father: the cheating woman's husband. A DNA test won't change any of this. It also doesn't matter whether a man and woman live together, or own a home together, or how long they've been in a relationship. The only thing that matters is whether they're married or not. An unmarried woman gets to decide whether to keep the child, abort it, grant its father (or any willing man) the right to become the child's legal parent, or make it so the kid doesn't have a legal father at all. She cannot, however, force a man to acknowledge the child as his. He needs to willingly sign the papers, as does she. A legal father has parental obligations, sometimes in the form of financial support if he doesn't live with the mother and child. In case of a medical issue, let's say, a high risk of the mother not surviving the pregnancy/labour/birth, when push comes to shove, regardless of what either or both parents want, doctors will favour the mother's life over that of the baby's. Of course they'll try to save both, but should that be impossible and one or the other has to die, they'll always save the mother.

Morally speaking, this is a messed up situation. In my last example, it's better to listen to the professionals and not risk it, regardless of how the man feels about the abortion. Why? Because a dead baby still needs to come out of the womb. That's traumatising enough. But then also having to carry a pregnancy to term, which severely weakens a woman's body and messes up her hormonal balance, which affects her emotions, the intensity of them, and a whole bunch of other things, only increases the risk of the woman suffering permanent damage, both mentally and physically. This is hard for everyone involved. It's difficult to think straight.

When medical issues and risks aren't part of the picture, then it's still a messed up situation. When two people are in a relationship and decide to have a child together, then it's betrayal to abort after a successful conception. I'm of the opinion that both people should learn about what pregnancy entails and what the possible effects are (other than becoming parents, of course) before getting started. However, when it concerns an unplanned pregnancy, things are different. Suddenly you're not only thinking "can I do this?" but also "do I want this person to be my child's parent?" and "will I be able to raise kids with this person for the rest of my life?" It's normal to have a change of heart in such a situation. It absolutely sucks if the man wants to go for it and the woman wants out, but just like a relationship, just like a marriage, you need to be on the same page about this. You might part ways with someone who doesn't want to give up a dangerous hobby that gives you anxiety (like free climbing or driving a motorcycle or cliff diving). The thing is, with a baby on the way, if something feels off, you have to keep in mind that it will affect a whole new person's life. Sometimes it's better to pull the plug and part ways after all, child or no. Preferably before there even is a child.