Speaking as a parent...there's a lot more to "caring" for a child than being pregnant and giving birth, way way more. It's sacrificing huge amounts of time, money and freedom that you could have spent on other pursuits, some of them 'selfish,' some of them potentially very beneficial to others. It's working together with your partner to decide who's going to be responsible for what, what your goals for your family are, and how you'll maintain your relationship despite the new stresses. It's staying up all night with a sick child to ease their pain a bit when you've got three classes to teach and two meetings to chair the next day, and spending much of what could've been both your free time and your work prep time doing things your kids want to do instead. It's being ready to drop everything in an instant, no matter how awful your day was or how tired you are or how much you've still got to do, because your child needs your direction or help or reassurance right now. It's thrilling in the excitement of watching a growing mind and heart and personality unfold, despite all the disappointments and disasters and moments of alienation and letting go along the way. I could go on and on...But, anyone who isn't able to provide these things shouldn't do it; parenthood isn't meant to be punishment, nor a child a whipping boy for all your accumulated resentments and failures of responsibility. If a woman wants to and is able to offer herself as surrogate mother for free, which is all planned infant adoption is, then great, let her do so. But that's no more 'what Nature intended' than being able to have an abortion is, and either way, the fact that it's voluntary is what distinguishes it from making a woman's body government property.
My mother was never pregnant with a child she didn't want, but she did seriously consider having an abortion when she was pregnant with me, because she had a uterine tumor at the same time and her doctors weren't sure she could 'do' both safely. I have never been bothered by this.
If I'd never been born, there wouldn't be an 'I' floating around out there whinging about it, and I'm not so arrogant as to think the world wouldn't have marched right on pretty much the same without me. I measure my mother by the kind of parent she was to me all the years I was growing up, not by whether she decided she wanted and was ready enough for another baby 36 years ago to take a medical risk.