In my own perspective, apart from rape cases, ignorance, health issues and other situations that risks the life of the mother, every man or woman must learn how to take full responsibility for their actions. If you don't want a baby then use pregnancy prevention medications or protections.
Aye, that's all well, and good. However, and this is where it becomes a little bit confusing, and there really in my opinion isn't a right answer, but what if you're using birth control, protection, but you don't want to permanently tie the tubes or cut the important parts? No contraception is 100% effective, meaning that there's a small chance you might fall pregnant, and while most contraception is effective in the >95% range, that 1-5% chance is actually very large when you consider the amount of people. According to this:
64.9% of the 72.2 million women aged 15–49 in the United States were currently using contraception.
that's a huge figure, and even if you take in 1% of that figure, that's like hundreds of thousands of potential unwanted pregnancies. That's huge, and those people were taking responsibility, and trying to avoid it.
While, I will definitely admit this is a rather moral grey area, I do tend to go along the lines of what o_e_l_e_o was alluding too , and when the conscious specifically develops. I'm most definitely pro choice, up until that point. That amount of time, is usually enough for people to get an abortion without too many issues. However, the issue which a lot of people don't talk about (mainly because it's a horrible thought) is those stuck in abusive relationships, which might not be able to get an appointment to actually get it done before then, which I don't know the answer too, but it's an horrible thought that this very likely is happening.
You could argue that there's a way to up that protection even further by both partners using protection, and taking medication i.e the women takes birth control, and the man uses a condom. That would effectively bring that protection level up, however there will still be instances of unwanted pregnancy, despite taking that due diligence.
Unless, you're insisting that those that don't want children, commit to a period of celibacy, which could very well bring up its own problems. I'll leave that for another day, though.