Tax rate (not amount), benefits, and garnishments (except child support) should be based on an employee's first 40 hours of work. Many Americans don't work extra hours because they pay a larger portion of the extra earnings in taxes. People with garnishments often work second, lower paying jobs because the second job is exempt from garnishments. Some people refuse the extra hours due to fear of losing benefits.
Benefits:
Government: Despite lower rates, generates more absolute revenue without having to cut spending.
More money in the hands of the middle class drives consumer spending.
Middle Class: Money trickles down much faster.
Poor: Ability to earn extra money without consequence of losing benefits. More social mobility.
Business: Ability to meet demand without future layoffs