Do Americans "earn" their incomes?

Steve Antler highlights the divide between liberals and conservatives on economic policy with a simple question:

First is the issue of everyday life's basic "fairness." Ask the question: under normal/average circumstances do people generally "get" what they work for or deserve? If you say "no" you're a Democrat. And if you're brave enough to say "yes" you're either a traditional economist or a conservative Republican.

In concentrated form this issue separates opponents and proponents of the inheritance tax. Bequests are the accumulated net sum of a lifetime's work. Do these sums represent legitimate private property or something akin to -- well, theft?