I've generally taken the approach that if you don't REALLY want kids, you shouldn't have them. Now, accidents do happen, and
sometimes often they're the best thing that ever happened for the parent(s).
But, for Mrs Skibum and I, we were both very willing to have a kid or two if the other one really wanted one, but neither of us ever felt that way. So we never did, and we made that decision permanent a few years ago.
Still remember a comment by a couple, both of whom had incredibly accomplished careers, and they were celebrating their 50th anniversary. Inevitably, someone asked the key to a couple having and balancing high pressure/power careers and still being happily married 50 years later. They were pretty blunt: "we didn't have kids."
I actually think that is more of an indictment of our society's lack of support for parents than anything else (at least one parent's career always gets harmed), but it is the reality we live with.
Anyway, I can wrap it up in a lot of logic about cost, and environmental impact, and what not, but I still think it boils down to "if you don't want them, don't have them."
The sacrifices are too much if it's not something you really want, and you'll be bitter about that - and something will suffer as a result (you'll be a less than ideal parent, spouse, friend, or employee). In my observation 90% of the time, it's the spouse that bears the brunt.
Anyway,
@Bread and other allbuffers that are young and still navigating this, get on the same page about this with any potential partners, and don't be surprised if your feelings change. "Yes, I would do this for you," is a legit reason to change your mind.