I think the answer to this is quite personal. I mean I do understand that you are asking why people think other woman should have children willy nilly, and I really don't get it either. It should be a personal choice and long thought through. After all children have no knowingness or choice to being born. They aren't appreciative of their mother's most of the time it seems, all the labour, hard work, and ruined body image. Is it really that worth it?
Well, I think that if the choice is to have a child one day, logically my mind says "Don't have any kids", they're expensive as a trip to hell, but in all the light of things having children is quite a personal journey of unconditional love.
You have to love children to want to have them and love them unconditionally, otherwise they are just expensive. If I cared more about my wallet, I would never choose to have them. Even by the time I am financially ready, raising children is still a journey. No one will ever truly be ready to be a parent, but there are people who want to take the risk of their life and that to me is a beautiful thing.
I could go into how it is just a poor decision but I want one of my own someday too much to go into how there are too many in the world already, and teaching them wisdom so they don't turn into hoodlums, blah blah blah.
Anyways, when it comes down to it, it is personal choice. No logic included.