If you want the option to stay home and raise your own child during their formative years (especially important during the first few years of life), you need to have more income than $25,000. It's a matter of practicality.
Of course, I realize that a lot of younger people don't think a child actually NEEDS a parent to care for them anymore.
BTW - even if you are willing to stick your baby with a sitter all day, child care is so expensive, a woman would need to make a good deal more than $25,000 for it to make financial sense to go to work, at least in California.
The reason it has traditionally been the male's responsibility to earn the money is because he has a greater ability to earn, and greater opportunity to advance in his career (unless he's an oaf) while women usually are the ones caring for children, missing days of work when the kids are sick, taking leaves of absence to give birth and care for newborns, etc.