Arguments against implementation
It has been argued that progressive taxation violates the principle of equality under the law.
Progressive taxes lower savings rates. High-earners have a lower average propensity to consume, so shifting the tax-burden away from them will increase the aggregate savings rate, which should increase steady state growth (if the savings rate is initially below the Golden Rule savings rate).
The classical argument against progressive taxation runs as follows:
The diminishing returns argument applies to the fraction of income used for present consumption. As income rises, diminishing returns implies that a smaller and smaller fraction of income will be spent on consumption goods. The remaining income will (of necessity) be used to purchase capital goods. This acts as a form of positive feedback that in turn yields more income for capital spending. Meanwhile (and because) these capital goods induce a decline in the costs of production which has the effect of raising real wages generally and implicitly raising the general standard of living. The income paid back on the capital helps create the disincentive to consume that creates capital spending. Thus, those capitalists who effectively manage their property are rewarded and given control of more (newly created) property, of which they are increasingly less inclined to consume and increasingly more inclined to purchase capital goods and thus further elevate the general standard of living by driving down the costs of production. As they acquire more capital goods, eventually their ownership outstrips their ability to manage and oversee what they own; however, they only control as many capital goods as can be attributed to the income of their prior capital---which previously did not exist. Therefore, their ownership does not negatively contribute to the general standard-of-living relative to counterfactual state of them not purchasing those goods. It would thus be misleading to argue that redistributing their capital may yield further increases in the standard-of-living. Doing so may well cause that effect, but doing so neglects that it was the assumption that redistribution would not happen that induced the accumulation of capital. — Eugen von Böhm-Bawerk, Karl Marx and the Close of his System, 1896
A belief that progressive taxation shifts the total economic production of society away from capital investments (tools, infrastructure, training, research) and toward present consumption goods. This could happen because high-income earners tend to pay for capital goods (through investment activities) and low-income earners tend to purchase consumables. Smithian and neo-classical growth theory says that spending more on consumption goods and less on capital goods will slow the rise of the standard of living, and possibly even reduce it since capital goods increase future production possibilities.
Brain drain and tax avoidance. High progressive taxes may encourage emigration because taxes are not internationally harmonized, so very high earners are sometimes able to relocate in order to pay less tax, or find tax havens for their income. Unlike the opposing income effect and substitution effect of leisure which may make tax progressivity neutral in terms of working hours, the emigration rate can only increase with the top rates of tax.
The differential in the higher rates of tax between the United States and Europe are cited as a factor in the "brain drain" of high-earners to America in the 1960s, and is considered an important influence on modern "economic migration."
Increase in tax loopholes such as income splitting techniques. This creates an incentive for business owners to split their business into smaller, less efficient ones for a lower tax bracket. It also encourages production from less efficient smaller businesses than larger ones.
The increasing energy expended on tax avoidances which occur with greater progressivity produces an increase in the work of accountants and lawyers. Because tax avoidance creates no net wealth this work is unproductive, and can make taxes on the rich less efficient than on the middle class, who have less motivation to exploit tax loopholes.
Progressive taxes are argued to create work disincentive. Consider again someone who makes twice the minimum required to live on, but pays all income above the minimum living threshold in taxes. Such a person had no monetary incentive at all to try to increase his or her income above the base level.
Justice in representation. Economic equity is sometimes used to argue against progressive taxation, on the grounds of representation being out-of-proportion to taxation: While the top 5% in income in most countries pay over half the taxes they only have 5% of the voting weight. This argument can be reversed into the plutocratic case that if tax is to be progressive it should be accompanied by greater say in elections for those who contribute most.
Policymakers are argued to be under a pressure from lower and middle income voters to limit higher incomes by the means of progressive taxation. A few economists argue against inequity aversion: "If policy makers' primary goal is … economic prosperity for all, they should avoid focusing on the politics of envy." (Gregory Mankiw)
A study from the libertarian Institute for Policy Innovation, which aims to reduce government intervention in the economy, has concluded that progressive taxes fail to decrease real income inequality.
Some[who?] libertarians, especially anarcho-capitalists, argue that only poll taxes can be economically efficient in the fullest sense (the utilitarian view), and/or that equity requires each citizen to pay the full exchange value in trade for governance services such as the guarantee of property rights
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