With this administration, it does not matter to them if everyone paid a flat tax because they would still say the rich were not paying their fair share. Their reasoning is that let us say 15% is unfair on the lower class because they would pay a relative larger amount per their total income that the person who makes one million or more.
Income of $25,000 flat 15% tax = $3,750.00 paid in taxes with $21,250.00 left.
Income $1,000,000 flat 15% tax = $150,000.00 paid in taxes with $850,000.00 left.
Each person paid 15% but the lower income individual only has $21,250.00 left while the wealthy person has $850,000.00 left. According to the left this is unfair because the person who makes more has more left over after taxes.