This isn't something you need to believe or not believe. The stats are in, decades of trickle down have not had the intended effect and various sources have shown this.

It's a pretty well supported fact that lessening the tax burden on the mega rich doesn't cause them to go opening businesses and it's surprising people ever believed such nonsense. Why would a rich person take a risk on a new business venture when the a fund can provide a steady, predictable return year after year with very little downside?