Josh Barro advances it:
[A] Buffett Rule would not simply mark a return to a time when tax burdens were higher on people with high incomes. It would entail enacting a new form of tax policy not used in other major countries and not used for any sustained period in the United States. It is very cavalier to contend that such a policy would not discourage investment.
Reihan guesses that "the Obama administration has no intention of actually implementing something like a Buffett Rule" and thinks "it has the trappings of an idea that is meant only for the campaign trail."