My fundamental principle is that we are all created equal, but we are all different.
Men and women are different, and women have a very specific obligation to make sure the human race continues to exist. Sure, men are necessary too, but I'm not sure that I would call man's participation an obligation. A man can be the father to 10, 20 or 100 children, for a woman even one baby has a permanent physical impact on her whole body.
What does equality mean, when women have collectively such a hill to climb? Shouldn't men have a hill to climb? How could we even the balance? Perhaps we should study the lifespan information - women live longer than men, right? Here's a quote from Eurostat, the European Union statistics agency...
In 2021, the number of healthy life years at birth was estimated at 64.2 years for women and 63.1 years for men in the EU, this represented approximately 77.4 % and 81.7 % of the total life expectancy for women and men.
So one year's difference, but on average each woman must produce the famous 2.1 babies to renew the population. Total life expectancy for women is significantly higher, but they don't enjoy it.
We could imagine a perfect world where womankind are rewarded for their obligation, where their work career is not affected, where childcare is free, where having a baby is such a small interruption on the scale of your whole life that its inconsequential. No really, that's what needs to happen! But imagination isn't reality. Generally laws do protect women, but if you have to turn to the law, you've already lost. Places in a crèche are limited, babies get sick, generally for the first few years the mother is under stress.
In a fair and equal world, men would share an equivalent burden. What mechanism can be used to create a burden equal to carrying a baby for 9 months, giving birth, and then giving personal care for generally another year? Well many governments are only too happy to invent a new tax!
Who would be taxed? Obviously not the mothers. Would all women escape the tax? What about sex changes? It might be difficult to define the exact criteria, which is an indicator that this is probably a bad idea.
What amount is taxed? Well collectively women are supposed to produce 2.1 babies, each baby represents at least one year of work, if we work for 40 years then the tax should be about 1/20th (or 5%) of each man's income. Yes, women spend 5% of their working life saving humanity!
On the other hand, this revenue could have an effect of lowering the rate of taxation in general, so women's taxation decreases by 2.5% while men's taxation increases by 2.5%.
The proposition is not practical but its an interesting thought experiment.