We do already have this problem with high marginal tax rates (counting the drop in available welfare as part of that 'marginal tax') at the border between unemployed/low-income/middle class. This article gives some good examples of where it happens currently: http://www.heritage.org/research/reports/2013/01/effective-m...
The other side of that same problem is that people who fall into lower levels of income have a very hard time proving they deserve access to the meager welfare programs that keep the permanently destitute from burning down society in a fit of lumpenproletarian rage.
