We can't have a progressive income tax because it unfairly punishes talented, hard workers like Bristol Palin:

Tax documents show unwed mother Bristol Palin earned more than $262,000 for her role in helping raise awareness for teen pregnancy prevention in 2009. ...
"If I can prevent even one girl from getting pregnant, I will feel a sense of accomplishment," she said at the time.

One prevented pregnancy at a cost of $262,000 would not be a terribly effective investment.