But "virtual currencies" are fully legal to exchange with USD. Purchase Facebook Credits for cash. And perhaps this could be an exchange for just non-monetary currencies. Credits for Credits.
You're letting your wishful thinking override your critical thinking. You can purchase Facebook Credits with cash just like any good, but you cannot easily convert them back. It's not a currency exchange; it's a purchase.
Unfortunately the law doesn't always make logical sense. The real question is, do you think the government will accept the full use of an untraceable, uncontrollable, hard-to-audit, hard-to-tax alternative currency without any kind of opposition?
I agree. Theres also barriers with banks/exchanges getting in the way and lobbying a startup out of existence.