The Generalized Henry George Principle:
One of the general principles of taxation is that one should tax factors that are inelastic in supply, since there are no adverse supply side effects. Land does not disappear when it is taxed. Henry George, a great progressive of the late nineteenth century, argued, partly on this basis, for a land tax. It is ironic that rather than following this dictum, the United States has been doing just the opposite through its preferential treatment of capital gains.