A decade or two ago I picked up a slim volume titled An Anthology of Pieces From Early Editions of Encyclopædia Britannica, published in 1963. On p. 47 I find the following item by economist J. R. McCulloch (1789-1864), from the 7th edition (1830-42) of the Britannica, explaining why a tax on income wouldnt work, because no people not altogether enslaved would put up with the odious inquiry into the affairs of individuals that would be needed to make such a program workable:
Taxation of Income Impracticable
The difficulties in the way of assessing income are of two sorts: 1st, The difficulty of ascertaining the amount of the annual revenue of different individuals; and, 2nd, Supposing that amount to be known, the difficulty of laying an equal tax on income derived from different sources.
It would be useless to dwell at any considerable length on the first of these heads. Incomes arising from the rent of land and houses, mortgages, funded property, and such like sources, may be learned with tolerable precision; but it neither has been, and, we are bold to say, never will be, possible to determine the incomes of farmers, manufacturers, dealers of all sorts, and professional men, with anything like even the rudest approximation to accuracy. It is in vain to attempt to overcome this insuperable difficulty by instituting an odious inquiry into the affairs of individuals. It is not, indeed, very likely that any people, not altogether enslaved, would tolerate, in ordinary circumstances, such inquisitorial proceedings; but whether they did or did not, the result would be the same. The investigations would be worthless; and the commissioners of an income-tax would in the end have nothing to trust to but the declarations of the parties. Hence it is that the tax would fall with its full weight upon men of integrity, while the millionaire of easy virtue would well nigh escape it altogether. It would, in fact, be a tax on honesty, and a bounty on perjury and fraud; and, if carried to any considerable height to such a height as to render it a prominent source of income it would undoubtedly generate the most barefaced prostitution of principle, and would do much to obliterate that nice sense of honor which is the only sure foundation of national probity and virtue.