Ok, so I'm going a bit off topic here but there would also be an issue where people can't know what other traders are setting prices at (because those kinds of websites are illegal). If you are going to buy something in a competitive market then you usually research which alternative gets you the most bang for your buck. How would this be accomplished?
Look at what price in Bitcoin things are being sold at anywhere in the world, look up the dollar value of those goods being sold for Bitcoin, and there's your going market rate. Even if Bitcoin becomes 100% illegal and subject to a bloated federal War on Bitcoin, it will still be legal for people to publish going exchange rates.