I couldn't find where I had heard it.

Basically, imagine a world where the United States had been conquered by the Soviet Union and there had never been a US income tax. The conquering Soviets wanted to punish the capitalist Americans so they implemented a series of fines for people who made profits. Naturally, they would fine greater earnings more than lesser and they'd punish speculation especially hard.

I forget all the details, but the point was that the current tax system is consistent with a complex communist punishment.