If one day I notice that I want to have children, I will have to weigh that against well-supported research that shows having children decreases happiness. Even if I feel that I very strongly want children, I would consider that to be very weak evidence that I would go on feeling so for 20-30 years (time needed to raise child to independence). The evidence of the research would be more weighty than my own feelings.

(Anecdotally, what I actually feel is that having children is utterly horrible.)