My former boss got divorced over this. He wanted children, she didn't. I don't know if this was discussed prior to their marriage, but it's entirely possible that one of them changed their mind later.
And sometimes they both change their minds. I know a couple who first decided not to have kids, she had never had them, but he had grown children and was considerably older. He happily let her change her mind later, they adopted and they adapted to the change really well. The main consideration on such a life changing decision, is that it isn't pressure at the risk of losing the marriage. Decisions made under threat are always resented.
DH and I nearly split up over this as well. We're 12 years apart (me younger) and when we first got together (I was 28) he wanted them and I wasn't ready yet. Then there was 10 years of dealing with his newfound substance abuse problem (long LONG story), then when I finally got him cleaned up and wanted kids he didn't anymore. With him at age 50 I can't say I could blame him.
The "selfish" label makes me want to throw up. I intentionally didn't bring any into a marriage that was in real rough shape, with one partner who was baked out of his mind 90% of the time, on the brink of divorce for 10 years, and I'M SELFISH? Bollocks. I did a kid a big favor by not dragging them into that situation.
I've (mostly) made peace with the situation - sometimes in life you get the present, sometimes you get the box, but the continued chastisement from the "you're selfish" crowd can be painful beyond belief.
LQ