I've heard it multiple times recently on Diane Rehm's radio show. A "Buffett Rule" like the one President Obama proposed in his State of the Union Speech would mean taxing capital gains at a 30% rate, and would kill off investment.
Such claims are nonsense.
Mitt Romney and his buddies aren't the only investors in the market. What Obama proposed in his speech was making sure that people who have more than a million dollars of income per year pay an effective tax rate of 30%. Yes, this would mean taxing the capital gains of a few at a 30% rate. But many of us who make less than a million a year have capital gains, and those rates can remain just as they are under a Buffett Rule.
This is a good thing for capital markets, because it favours having a larger number of investors, rather than a handful of disproportionately large players. Putting the decisions in the hands of a select few is never the best way to allocate resources; any fan of Adam Smith should agree.
So don't let anybody get away with saying that a Buffett Rule makes the capital gains tax rate 30%. When you hear that, ask them if they made a million dollars last year. There's a 99% chance they didn't.