Emily , I have no doubt that having children gives those who wanted them badly a sense of satisfaction. I agree that day-to-day happiness is not the only measure of life worth taking into consideration. But I do think brandishing happiness studies on the issue is an important public service; we can't have too much information when making an important decision like whether to have kids.
Perhaps it's because I have a background in sexual-health advocacy writing, but I tend to look at issues like this through the risk-assessment lens. Effective education around sexual health is rarely about telling people no or issuing hard-and-fast rules, since it quickly became apparent that people are going to have the kind of sex they want, even if you scold them for it. It's about giving people full information, so they can do a cost/benefit analysis. It gets comically detailed sometimes, with HIV counselors taking the time to explain to clients that it's probably best to hold off oral sex after you've eaten pizza that burned the inside of your mouths.
There's so much pressure in our society not to talk about the very real risks of child-rearing, usually because of superstitious fears that talking makes it true. But I tend to think that it's best if people walk in with their eyes wide open. If you know that the risks include strained or terminated marriages, constant stress, and the inability to move about freely for many years, and you decide those are risks you're willing to take, then that's great. And I certainly believe the sense of satisfaction will outweigh the headaches for that person.
On the flip side, I think it's important that people unwilling to take these risks avoid them. It doesn't do children any good to be born to parents who find that they're in way deeper than they could have ever imagined and whose stress and resentment levels are remarkably higher for it. Pointing out that having children gives you more opportunities to bicker, for instance, might be meaningless to a couple that doesn't bicker, but to someone who knows she's short-tempered, that's valuable information to take into consideration. I'm happy to see that choosing childlessness has become normalized for this reason; far more people who don't really have the stomach for child-rearing aren't imposing themselves on helpless children out of a misguided sense of duty.