Not quite. The first dollar will have the same utility regardless of source. If you believe wealth has a diminishing marginal utility, like any other good, there is a real difference between the first and billionth dollar. Taxing them at the same rate is a higher burden on the former. Obviously utility is a nebulous concept, and if you believe wealth has constant utility you won't agree with it. But assuming diminishing marginal utility of wealth, what you call inconsistent is consistent.