Flat taxes hurt the poorer income brackets more than anything else. That's why it is a progressive taxation system. Those in the lower income brackets are much more sensitive to income changes when it comes to purchasing necessary goods and services. As a household brings in more income they are increasingly less price sensitive and will be able to make their dollars go further, so they can be taxed more. Deductions help encourage growth and improve infrastructure as well. For example, if you install solar panels in your home you get a deduction. If you buy an electric vehicle you get a federal tax credit. I think these things should be encouraged. And because there is an initial cost to do these things and they are somewhat nontraditional there needs to be an incentive or else it would not take off in the general public. And you also need to encourage people to invest, to have a 401(k), to have a health savings account, and a retirement plan. These things aren't taxed (to a degree) or else no one would put their money into them. There needs to be an incentive to encourage growth and tax credits is how it happens.