Don't have kids if you make that little.
I don't disagree with you about that, but it's really not my point.
Single guy making 20K has to eat, buy clothes and travel to and from work, grocery stores doctors, whatever.
Single guy making 200K has to do the same.
Guy making 20K spends 5K on food, clothing, medical, gas whatever.
Guy making 200K spends the same.
Both guys pay about 28% in taxes.
20K guy = 5K + 5K = 10K in total taxes which is 50% of his earnings
200K guy = 5K + 50K = 55K in total taxes which is 27.5% of his earnings
So if 20K guy didn't have to pay 28% and instead paid zero he'd be out 5K total of his 20K earnings. Which is 25% and is much closer to the guy making 200K.