I have to say, I was sympathizing more with the husband until the rhythm method came up. If your birth control consists of something with a 9% per year failure rate when done perfectly, you sort of lose the right to be shocked.
That said, I’m a little surprised at the reactions of other posters (pre-rhythm-method-mention). Maybe it’s just that I’m from the Godless Northwest, but to me, if you’ve talked about waiting to have kids, I take it as written that an abortion would be the reaction. It’d certainly be what I’d expect if my girlfriend got pregnant (and maybe we should have a little talk… you people are scaring me). In fact, I think my reaction to her wanting to keep the baby would be roughly on par with some of the reactions upthread - ‘she said WHAT?’. Simply put, while I’ll support a woman’s right to choose legally, as a couple, I don’t think it’s fair to give one party more control in what should be a shared responsibility, and if your previous discussions led to ‘no kids now’, I’d expect that to hold.
Granted, wanting the other party to come around to your way of seeing things is natural, and I’d expect both parties to feel that way, but I think it’d be folly to think that he’ll ‘come around to the right way of thinking’. Personally, in his shoes (and again, ignoring the rhythm method business) I’d be pretty upset that I was being pressured into a pretty damn big choice - and one that was already decided, no less. If that makes me cold, maybe I am, but I don’t actually see anything wrong with abortion, even for convenience’s sake. Potentially frivolous, perhaps, given that pregnancy is not assured later in life, and certainly with a risk of psychological trauma that should be considered, but not morally wrong, or even morally ambiguous.
In your case, I think the choice of the rhythm method indicates either some desire for children, or some level of boneheadedness. The initial abortion stance may have been sheer reaction, and he may come to want to have the baby, but I’d be veeeeery careful about not urging it. If he does come around, it needs to be because he wants to, not because he feels pressured. I’d go so far as to not even bring it up unless he wants to talk about it. But I wouldn’t expect that he’ll change his mind - boneheaded decision or not, he may just not want kids right now.