So you're happy to subsidise those people who deliberately stay under the threshold, claim benefits so that they can work part time and spend time with their kids. But you're not happy if higher earning women, (who are equally doing important jobs, would also like to have bigger families, but don't, because they can't afford big families) get a tax break, because they're not then paying into the system of those who could work more, but don't.
So really what you're saying is lower earners can have big families and the tax payer can pay for it, but higher earners can't have big families and get tax breaks to enable them to do that, because they need to pay for poorer people to have that instead.
Got it.