In some cases yes.Do you think people work for $40k when they can earn $70k? Usually those couples where 1 person can earn $70k are in a higher socioeconomic class than those where both can earn $40k. It is a form of consumption to have a stay at home spouse due to home production. I know conservatives want their wives barefoot in the kitchen--don't moan about how the tax system should be biased against min wage earners to support their middle-income lifestyle with a stay-at-home spouse,
I know a few families where they stuck to jobs and areas where they were both making a modest salary, rather than relocating/changing to a different job where it would be a substantially higher salary for one of them.
Also some of the higher salary positions typically were more demanding, and that spouse would be less available for child care. This is quite common in shiftwork, like for nurses or autoworkers. The spouse has to take a more flexible job to accomodate it (which pays correspondingly less)
I'm not sure what your last statement is even trying to say
I just think that if government support benefits and programs are based on family income, then taxes should be paid based on family income. It is not fair that households with the same income will pay different amounts of taxes, and get different levels of government support.