Well, there are several US laws against exchanges. Check out some of the US securties laws as well as money transfer agent laws. Money Laundering is a major issue in the US, and exchangers like those who exchange Liberty reserve and other ecurrencies are not permitted to operate in many cases.
Why are you trolling our forum?
If you don't exchange bitcoin's using LR, than there isn't any problems. Actually this whole "exchange" aspect of bitcoins sickens me. Thats not what they're meant for. Go back to "talk gold" and spread more HYIP speculation, on a currency that simply isn't going anywhere. No matter how much clowns on the Internet try to make it go away.