The Bitcoin community's already gearing up for this to be the end of Visa/MC if it passes. Once they're forced by fiat to shut down their largest clients and put in a squeeze between continuing service or getting sued by the RIAA, capital will go elsewhere. This could be sort of, to the American economy, what the Iran/Iraq war was to authoritarians in the middle east; great way to spend energy while the civilized free world passes you by on the highway.