> That single responsibility in this case is to make a contribution of our income to fund the government, period.
Yes. And as part of that you have to decide how much each person is to contribute.
> We should have a simple tax formula strictly dedicated to funding the government where everyone has skin in the game
Yes.
> ..and contributes equally along some metric.
Yes, according to their means. The metric is contribution proportional to your ability to contribute and that folds in implicitly the idea that your "means" are non-linear with respect to marginal utility. Noblesse oblige. [1]
> The flat tax seems a dead simple reasonable metric and is unquestionably equal when focused on contributions.
No, it is not. Because 10% of 10K/yr income of someone working at burger king is an undue hardship whereas 10% of 1M/yr income of someone running a big company is no burden at all. 1K to someone making 10K may be the difference between sleeping in a bed and sleeping in the street, but 100K to someone making 1M, frankly, they wouldn't even notice it.
> Once we start trying to equalize along these other dimensions of marginal utility or equality of some other thing we're no longer focused on funding government but enacting some equality/justice endeavor.
No, we know how much we need to fund the government based on cost of policies enacted. That's not the job of the IRS, that's the job of the budget committee in congress. What the IRS is doing is figuring out how to apportion that burden among the population.
> Those I imagine probably also suffer from holding no simple formula to calculate their equalities against. Let such endeavors be handled by some other government agency dedicated to those causes, why drag the tax system into the mix and complicate things is what baffles me.
Again, the goal is to figure out how to apportion the burden, and that's done by indexing to marginal utility, bringing us back to where we began.
To be clear this isn't coming from someone looking to take from others, I'm in the top marginal income tax bracket, and I think it should be much higher than it is. IMO it should go back up to 70% as it was for much of the 1900s. [2]
[1] https://en.wikipedia.org/wiki/Noblesse_oblige
[2] https://www.washingtonpost.com/us-policy/2019/02/27/top-tax-...