It is not just irresponsible people who get pregnant unintentionally; and even those who do not attempt to use protection may be forced to do without it. Not everyone can get free, confidential birth control; even if there is a place offering it, a person might not have the support/safety/funds/mobility to get it. Even if one does get condoms, one may be pressured or forced into not using them (when the sperm-carrier says "but it feels better without a condom, pleeeease" or refuses to wear one, or fakes using it (which has happened to several of my friends), and doesn't consider it "real sex" unless it's PIV). If that is the case, social stigma prevents saying so. Even if one is privileged enough to be able to get and use at least two methods of birth control, pregnancy is still possible. The condom can break or come off, the pill can fail, etc.
If sperm-carriers were required by law to take contraceptives once they reached puberty and had forced legal responsibility for their fetuses (NOT financial support but actual RESPONSIBILITY), if it was common practice for sperm-carriers who wanted the child to live to hire the pregnant one as a surrogate (if that one chose to say yes) and pay all zir expenses and then take the child, and if egg-carriers could get hysterectomies and/or remove their eggs if they pleased (including FUNDING for these things because otherwise contraception is a luxury of the rich.), then yeah, make abortion illegal except in cases of need. (then the government would be intruding on people's bodies, but at least it would be doing it more fairly) But the need for legal abortions by choice comes from the huge power difference which forces egg-carriers to bear the responsibility for contraception (even though it's usually safer for sperm-carriers to do so) often makes egg-carriers pregnant through force/coercion, creates a very dangerous and expensive environment for the duration of the pregnancy, and often forces egg-carriers to care for unwanted children through social pressure. The suffering of a baby is not worse than the suffering of an adult person, especially considering that the suffering of the baby is short, and the suffering of the adult can last the rest of zir life. I do not consider death to be the ultimate evil, to be avoided at all costs; it is a natural part of life, unavoidable. What can be avoided is an increase of suffering.
I respect life, but carrying a child to term is not merely respecting life -- it is suffering for another human being. In no other place does the government force one person to sacrifice and suffer for another (quite literally risking one's own life to do so!), and I do not think this should be an exception. There are many children without parents, and the government does not force people with resources to adopt. If you're going to call it a sacred duty it needs to be everyone's sacred duty, not just the "bad sluts" who had the misfortune to get pregnant when they didn't want to.
As far as my own morals go, I consider not forcing people to do things against their will to be a higher moral than protecting life. I can understand having those in a different order or not holding them, but it does not feel right to me.
As for myself, I don't know. I think I would want to carry to term and give it to a couple who otherwise couldn't adopt, but I have no idea what kind of pressures might exist in my life at the time that I accidentally got pregnant. I'm quite careful -- but it's still possible that I could get pregnant. I do not want to be forced to carry a child, to pay for the extra food and care, to deal with the risks to my own body, etc. If I sacrifice, I want that to be my choice.