I call bull on your your total shit:
a) many women like flexible jobs with lower hours because they actually care about their families
Shite; many of us are eager to climb to corporate ladder and have partners who want to take the burden of looking after the kids. Get your head out the 1950's because it's smelling awful.
b) In general, flexible jobs are in lower-paying job categories
Shite; see above. Flexible post childbirth shouldn't be any different from other sabbaticals.
c) women often take a career break to have families, which means they don't climb the corporate ladder to the higher-paying posts
Shite; See above. Why should be be penalized just for taking 3 months off after childbirth? I've seen many men take similar time off for such things, or for other reasons entirely. Don't see men being penalized for that.
Your post is oh so typical from men who don't have the ability to carry a child. We do, so now you want to punish us for that.
The only day this will all be straightened out is when men can carry children - then we'll suddenly see the rules change because we can't have men suffering, can we?