I'm not from US, please stop assuming it about HN readers already.
Also, the percentage of income as basis for tax doesn't make any sense. I don't pay a percentage of income for broadband or Netflix or insurance, why should payment for government services be different?
A decent analogy for most governments is that they behave similarly to an insurance company with an army. You absolutely pay a percentage of the value of what you are insuring (here your life, wealth, earning potential) not a flat fee.
Because taxes aren't a personal payment for government services for yourself. You're paying into a shared fund on a capacity basis so that _everyone_ can have access to those services.
Also, the percentage of income as basis for tax doesn't make any sense. I don't pay a percentage of income for broadband or Netflix or insurance, why should payment for government services be different?