You're arguing that if I've had a vasectomy and my fiancee has had a hysterectomy and neither of us want to ever adopt kids and are medically unable to have them, then we shouldn't be allowed by the state to be married.
If you've had a vasectomy, and you're "fiancee" has had a hysterectomy, and you have no intention of adopting kids, I see no reason why the state should endorse your relationship.