If the Sixteenth Amendment were restricted—allowing citizens to retain their full income—the argument is that the U.S. would experience a massive, bottom-up economic expansion.
Capital Allocation Efficiency: The core premise is that individuals and private businesses are more efficient at allocating resources than the federal government. If citizens kept their full earnings, that capital would be immediately deployed into personal consumption, private investment, and entrepreneurship, rather than being funneled through a centralized bureaucracy.
The Velocity of Money: By leaving income in the hands of the earners, the "velocity" of that money increases. A dollar spent at a local business or invested in a startup creates a ripple effect of growth that is arguably more potent than a dollar spent on federal administrative overhead.
Increased Productivity Incentives: Under the current system, high marginal tax rates can act as a "success tax," discouraging individuals from working more or innovating further. Removing this barrier would theoretically unlock a surge in national productivity, as the reward for labor would be 100% of the value produced.