As a general rule, taxation of returns on savings is always double taxation. Money today is not worth the same as an equal amount of money five years from now,

As a general rule, taxation of returns on savings is always double taxation. Money today is not worth the same as an equal amount of money five years from now, or an equal amount of money after it has been invested in a risky venture with a substantial chance of losses. Returns from capital are, in expectation, a compensating differential for such differences in value. Now, this is not to say that some taxation on savings isn't sometimes appropriate; for instance, some forms of investment are non-transparent and might be used to shield earned income from taxes that should bear on it; also, higher-income folks tend to save more and to choose riskier investments that yield higher expected returns; so returns correlate with ability to pay in a way that's worthy of note because it doesn't impact incentives too much. Taxes that bear on some peculiar assets, such as the land-value of urban real estate, EM spectrum rights, or investment into highly-polluting industries, also don't adversely affect incentives. However, existing taxation on capital appears broadly appropriate to take advantage of these things; the bulk of taxes should still fall on tax bases other than savings and investment, such as the portion of income that's not saved but spent on non-baseline consumption of goods and services.