Taxing as individuals is kind of unfair to single earner households, since the earner has to support more people it seems reasonable to tax them less. You could maybe accomplish a similar thing with deductions but there will still be some weird cases
As a mostly single earner in a community property state, my spouse earns half the income for tax purposes. If you were going to tax individuals, it's probably reasonable to apply income evenly across marriages for all states.
We have exactly this problem in the UK.
A couple each home earns x, each gets taxed on x. Each gets the tax free allowance on the fist £12.5k of the annual income. Each gets the full basic rate slice before they hit higher bands etc.
If one of the couple earns 2x and the other zero, then only one can use their tax free allowance and they get one slice of the basic rate band etc.
They still have the same pre-tax income for the same household.
Personally I think people should be allowed to opt in to sharing taxable income.