If Herman Cain has been harshly criticized for his 9-9-9 plan, which includes a 9% national sales tax, should we expect Robert Frank to come under fire? After all, on Morning Joe today, the Cornell University professor proposed a progressive consumption tax that could go to . . . 100% on the rich. Frank's notion is that the very high rates would discourage the rich from building "mansions" [a term he used multiple times during his appearance]. And the taxes thus collected could go for things he thinks we need. For example, Frank incredibly claimed that in the US, "we...