I think that whole line of argument is what gets us into the world that Intuit and H&R Block love, where we say, taxing charitable donations is "unfair," but who counts as charitable, but what about donations to your own foundation; taxing medical expenses is "unfair," but only in certain ways; taxing married couples is "unfair," but what about couples whose marriage isn't federally recognized but is state recognized, taxing the value of a research grant paying for a grad student's tuition is "unfair" if they're not even making as much money as the tax, but taxing in-kind donations generally is fair, etc. etc. etc. (It also carries with it the assumption that whatever wage you make in the first place is "fair" - that if you make $10/hour making food or $1000/hour laying people off, some process has already called that "fair" and you trust its results. There are, of course, arguments that this is right, but personally I think that's a little questionable.)
The purpose of tax policy IMO is to engineer the society we want to see. We want to see a society where government is funded decently. Not too little, presumably not too much either. We also want to see a society where people who do productive things do not say "Forget this, I'm out" and move elsewhere, so (for instance) a 100% wealth tax on assets over $1M is out. This clause starts to resemble a fair tax, because the most effective emotional argument is "You can't tax me like that, it's unfair." But that's not actually the practical argument. The practical argument is "If you tax me like that, I would prefer to uproot my life and move to another country" or "If you tax me like that, I will instead choose not to be productive in ways I would have otherwise been productive, and the cost to society is a net negative."
Once you think about it like that, it turns out you can tax the person who makes $1M/year significantly more than 15% before they threaten to move out, and certainly before they threaten to be less productive in meaningful ways (underemploying themselves, hiring fewer people, etc. - they're still going to have an inherent drive to do well for a while). So you have relatively little downside up to some percentage, and you have steadily increasing revenue for society. (Plus, as a bonus, you mess with the income inequality curve.) So you may as well increase that tax rate.
And there's an argument that this is, indeed, the most "fair" - otherwise you are letting money go underused, because the person making $1M/year doesn't strongly care, and an effective government program is underfunded.
I think that whole line of argument is what gets us into the world that Intuit and H&R Block love, where we say, taxing charitable donations is "unfair," but who counts as charitable, but what about donations to your own foundation; taxing medical expenses is "unfair," but only in certain ways; taxing married couples is "unfair," but what about couples whose marriage isn't federally recognized but is state recognized, taxing the value of a research grant paying for a grad student's tuition is "unfair" if they're not even making as much money as the tax, but taxing in-kind donations generally is fair, etc. etc. etc. (It also carries with it the assumption that whatever wage you make in the first place is "fair" - that if you make $10/hour making food or $1000/hour laying people off, some process has already called that "fair" and you trust its results. There are, of course, arguments that this is right, but personally I think that's a little questionable.)
The purpose of tax policy IMO is to engineer the society we want to see. We want to see a society where government is funded decently. Not too little, presumably not too much either. We also want to see a society where people who do productive things do not say "Forget this, I'm out" and move elsewhere, so (for instance) a 100% wealth tax on assets over $1M is out. This clause starts to resemble a fair tax, because the most effective emotional argument is "You can't tax me like that, it's unfair." But that's not actually the practical argument. The practical argument is "If you tax me like that, I would prefer to uproot my life and move to another country" or "If you tax me like that, I will instead choose not to be productive in ways I would have otherwise been productive, and the cost to society is a net negative."
Once you think about it like that, it turns out you can tax the person who makes $1M/year significantly more than 15% before they threaten to move out, and certainly before they threaten to be less productive in meaningful ways (underemploying themselves, hiring fewer people, etc. - they're still going to have an inherent drive to do well for a while). So you have relatively little downside up to some percentage, and you have steadily increasing revenue for society. (Plus, as a bonus, you mess with the income inequality curve.) So you may as well increase that tax rate.
And there's an argument that this is, indeed, the most "fair" - otherwise you are letting money go underused, because the person making $1M/year doesn't strongly care, and an effective government program is underfunded.