If you make $100 and I make $1,000, and we both have a 5% tax rate, equally, who do you suppose it hurts more?
You pay $5 in taxes and are left with $95 for the week. I pay $50 and am left with $950 for the week, so who is burdened more?
A flat tax harms the poor/lower middle class disproportionately because they spend a higher percentage of their income than the wealthy class.
Again, I'm shocked to find out, somehow, magically I guess, your views line up exactly with the GOP platform for decades..