From http://taxprof.typepad.com/taxprof_blog/2009/04/david-walker-why-.html:

Unless we begin to get our fiscal house in order, there's simply no other way to handle our ever-mounting debt burdens except by doubling taxes over time. Otherwise, our growing commitments for Medicare and Social Security benefits will gradually squeeze out spending on other vital programs such as education, research and development, and infrastructure.

Another great line: "...additional accumulations of debt are, absent dramatic reductions in the size and role of government, basically deferred tax increases."