Sure. When the federal income tax was instituted in 1913, all of the tax rates were individual (and the lowest bracket covered most Americans). People who were married could lump sum their income and divide by 2 to find the correct rate. Married filing jointly back then was just a way to save on paperwork and hassle. Lump the two incomes together, divide by two, and treat the two people equally. That was it.

In 1948, you got the official married filing jointly "status" and with it, the various income credits, deductions, etc. One would think that the married filing jointly tax rates would simply be double what the individual rates were, right? Wrong. The joint rates were about 1.8x the individual rates. Someone was 100%, someone was 80%. This being 1948, the woman in the dual income family was 80%. The IRS didn't want to appear to favor married couples over single people (even though they did), so they said 1.8X instead of 2X the individual rates. If you were lucky enough to be a big wage earning white male in 1948 America, you got a huge tax break since stay-at-home moms were the norm, there was a baby boom going on, and only about 20-25% of women worked.

Married filing jointly is silly. It should be a sum of the family income, divided by two, then mapped to the individual rates.

> One would think that the married filing jointly tax rates would simply be double what the individual rates were, right?

Certainly not, why would I expect that? That's mean that if there's a family of two paying individual rates, they pay X% of the income, but if they file MFJ, they pay 2X% of the same income, or twice as much. How would it make sense?

> The joint rates were about 1.8x the individual rates.

Do you mean the tax brackets and not rates?

> Someone was 100%, someone was 80%.

That is a weird conclusion - why not each one 90%, or one 110% and one 80%, or one 180% and one 0%? Having MFJ rate does not imply any distribution of income, not that I can see it at least.

> This being 1948, the woman in the dual income family was 80%

What you mean "was"? Do you mean average married woman's income was 80% of average man's income in 1948? Maybe (I have no idea, didn't check) but what this has to do with tax rates? If it was so, it was certainly not because of the tax rates.

> Married filing jointly is silly

No it's not. The fact is our society is organized around families. It's not everybody, but mostly that is how it works (and MFJ is optional of course, so if you don't like the model, you can stay away from it). Taxing family - or household - as one unit makes a lot of sense, because that's how the actual households commonly work, the income and the expenses are shared. Just as taxing a company as a unit makes sense, instead of taxing each employee's production individually, so does it make sense for a household.

> It should be a sum of the family income, divided by two, then mapped to the individual rates.

That's another question. Maybe specific tax brackets need to be adjusted, maybe not - at least this link suggests that MFJ has actually lower brackets (and thus higher taxes) than two individual incomes: https://en.wikipedia.org/wiki/Marriage_penalty

But: all that explanation failed to show where does it say "women make no money". It is true that in 1948 a lot of women did not make any money as employees, and instead were providing services to their families which weren't remunerated monetarily, but I see how having (optionally) the household as taxpaying unit implies "women make no money". It still makes no sense to me.