I guess this is a case of "if you understand, it probably doesn't apply to you": real marginal tax rates make work unrewarding for poor.
To say that antipoverty programs in the United States are perverted may be an understatement. When you take into account the loss of means-tested benefits (e.g., cash assistance, food stamps, housing subsidies, and health insurance), and the taxes that people pay on earned income, the return to working is essentially zero for those in the lower two quintiles of the income distribution.
For many of the working poor, the implicit marginal tax rate is greater than 100 percent. The long-run consequence of undermining the positive incentive to work is, of course, the creation of an underclass acclimated to not working; the supplement of cash and noncash benefits with income from crime and the underground economy; and the government resorting to negative incentives such as mandatory work programs.
Below, I show the relationship between earned income and after-tax income plus subsidies for a hypothetical Virginia family of three, consisting of one adult and two minor children. As you can see, the relationship is essentially flat from $0 to about $40,000 in earned income.
The point is that there isn't much reason for a poor family to work when every extra dollar they earn reduces the government benefits they receive by a dollar or more. It's hard to see how such a system benefits anyone, even the poor.