The argument is empirical. Very high top marginal income tax rates (not the same as taxes in general, which is not the topic ... sales taxes and other regressive taxes undoubtedly depress the economy) in the 1950s ... unprecedented prosperity ... Kennedy lowers the top rate which was on the wrong side of the Laffer curve and growth picks up ... then Johnson lowers the top rate again, overcorrecting, and the economy slows down ... it is raised again and growth picks up. Nixon lowers the top rate and we enter the era of stagflation. Reagan lowers the top rate and creates a temporary inflationary boom (while real revenues plummet), followed by decades of sluggish growth interrupted only when Clinton raises the top rate and years of higher growth and higher revenue follow.