I don’t think it’s realistic for a lasting relationship.
I’m envisioning this situation from the point of view of being a woman who eventually wants a child. I’m also drunk fluthering, so take what a say with that in mind. If I get pregnant and my guy doesn’t want a child, my body will change in ways he’s not excited about. If I had a child, my idea of how I should spend my time will change in ways he’s not excited about. My priorities will drastically shift in ways he’s not excited about. My future plans and finances will change in ways he’s not excited about. What’s the motivation for him to stay with me? How is this the relationship he signed on for? I’m not talking about an unplanned pregnancy between the two of us, as that comes with a whole different set of issues.
On the other hand, if he somehow had a child and I didn’t want to be a parent, the time and energy he spends with me will dramatically change. The plans for our future will dramatically change. If this were to happen, I’d be wondering where the guy I fell for went.
Committed relationships are partially about a shared view of life and common plans for the future. One member of the relationship having a child against the will of the other member changes everything, and I cannot imagine that change being a good thing.