That't total bollocks.Uh, no.
Restricting the ability to conduct transactions costs everyone money.
I understand what your ideology tells you. I'm reporting what the facts of history tell me. The U.S. economy grew more than twice as fast in terms of per capita GDP during the 40 years when income gaps were relatively narrow (1940-1980) than in the 40 years prior to that or in the 31 years since. Also, if you compare nations in terms of income equality/inequality and also in terms of per capita GDP/PPP, you find that the richest countries in the world almost all have narrow income gaps and low levels of inequality.
That's what demand-side economics would predict, because narrower income gaps mean higher consumer demand which drives investment into production of goods and services and so pushes up GDP growth. As such, it's a real-world empirical test of demand-side versus supply-side economics. Demand-side wins.
The period 1940-1980 was marked by the US emergence from WW2 as the only industrial power with an intact and up to date industrial base. Plus pent up demand from rationing and the baby boom all dictated rapid growth and prosperity. Income disparity had nothing to do with it. Of course 15 year olds don't make much money so that woudl go a long way towards reducing disparity.
Rich nations did not start out being equal. As countries' economies grow there are large disparities as some people make more money than others. Afterwards taxes rise and those who have made money are secure. The opportunity goes away for anyone else.