According to most studies, the rich currently pay somewhat more than half of all taxes. With a flat tax, they would still pay about half. When the government redistributes money via tax and other benefits, those who have worked hard and succeeded are punished to subsidize, in many instances, those who have possibly been irresponsible, lacking in ambition and even lazy. Responsibility is one of the aspects of freedom that is required if this country is to continue on its democratic path. Lower taxes mean, primarily, less government and more investment in private enterprise.
Lower taxes mean more money to invest, plus freedom as to where to invest it.
Less government equals less regulation and more freedom. I can personally cite instances of bureaucratic cost inflation. Then the county provided the services with the pittance remaining, utilizing a substantial portion in making reports to the federal government, the state agency and the regional agency. Apparently, these projects are currently under construction and the funding has been acquired. What is interesting is that the draft estimates for these projects are approximately half of what the consultants of the master plan for Jacksonville projected.