Also, don't you see how callous it is to worry about how a rich person has to pay country club dues, in the context of talking about poor people who struggle to afford food sometimes? Why would your sympathies lie with the person who has all of their basic needs met and is "struggling" only to utilize as many luxury goods (yachts, country clubs, sports cars, box seats) as possible?
However, there are two problems that I see. I suspect there are more.
First is that what you spend is only related to what you make. Specifically, it is relatively easy to find ways to not spend money if you have extra. What this means is that, at an absolute level of what you make, a flat tax actually gives a very easy way for high income people to have a lower tax rate. Turning it into "the more you make, the more you can proportionally keep." Which is sorta antithetical to the idea of the flat tax.
The second problem is essentially the cold start problem. Society is expensive to keep going. There is not much of a way around that. So, the rate will have to be relatively high to get the necessary funds. And this will hit those with low incomes harder than the ones with high.
I don't think either of these are necessarily road blocks to the idea. But, I do think it will necessarily get complicated.
I think you are missing the point. If it is truly a flat tax, the number of dollars you are taxed goes up (in a directly proportional way to the number of dollars you make). So you DO pay more the more you make. It isn't even a logically arguable point.
"a flat tax actually gives a very easy way for high income people to have a lower tax rate.":
-- again that's a completely illogical statement. If it is truly a flat tax *EVERYONE* has the same rate -- that's the very definition of a flat tax.If so, apologies. It is still easier for the wealthy to dodge. But not as easy. (Main way I can think of is that at that level you can often live off the company. I don't think this happens enough to care about. Could be wrong.)
This still doesn't address the cold start problem. If a region needs X dollars and that requires Y rate, how do you ensure that doesn't drown out the poor?
And again, I'm not pushing these problems as show stoppers. Just things that contribute to a complicated solution.
No one is going to refuse a salary bump because it will increase their marginal tax rate.
And moreover, how likely is it that they can increase their hours, but be paid exactly the same hourly wage?
I believe such people are extremely rare and as such this hypothetical disincentive isn't particularly relevant.