>It is rarely possible to start a business only with your own money that you saved.
People outside of the upper middle class strata usually don't have the opportunity to save significantly anyways after CoL is included in the US, and usually require a loan to start a business (or at least in every case of non-upper middle class business founder I've worked for).
Regular people would personally carry a relatively lower tax burden than a flat tax would require for them actually, and a progressive corporate tax in the US would likely result in them being more likely to be successful once they start their business.
Given that many pro-business states in the US have progressive income taxes to actually encourage reinvestments into small businesses (Carolina, Georgia, Alabama, Mississippi, etc..) and appear to be succeeding quite well in that regard, is there any specific reason you think a progressive income tax system that reduces the burden on regular people relative to a flat tax is a significant blocker for regular people to create businesses?
Looking at your description of the problem, it almost seems like you should be advocating for a *more* progressive tax system where burden is placed further up the chain with regular people maintaining even less of a burden.