I have to say that I think it's MUCH different in a situation where you haven't had children yet.
It would take A LOT for me to consider putting my daughter through that. The separate houses, going back and forth, going days without seeing one of her parents, spending holidays away from each other, dealing with step-parents, step-siblings... there are very few things that would make me choose that life for her. It would be an absolute last resort.
I have always wanted 2 kids, I'm an only child and I hated it growing up. I still hate it now. I would be devastated if my husband told me he didn't want another (and I know he'd be fine with just one and doesn't want another right now). But ultimately, is it worth bringing another child into the world at the expense of the child I already have? I really can't see how. My little one's happiness and stability comes first. I suppose if I felt I couldn't love my husband anymore if he didn't give me another baby then I wouldn't stay with him, but that would make me question how much I loved him in the first place.
If my husband had said, only 2 years after having our daughter, and after only discussing it for a few months, that he was willing to split our family up over it... I would be livid and extremely hurt.