Is a US-based exchange trustworthy? I have a feeling it'll exist at the mercy of the Feds.
US Federal Prosecutors are looking into the Mt. Gox failure. Regulation here will improve the confidence in Btc if anything.
While it may be outside the Federal Reserve's jurisdiction, there are many other federal agencies.
(Thought experiment: Obviously, if one did wield influence on a central bank after winning the rights to run it from a nation, one would try to keep public perceptions as wishy-washy as possible in order to keep pockets safely lined and one's fiscal hegemony in place.)