Ships follow the laws of the country they are registered in so even if the US legalized it would make little difference.
Very few ships are registered in the US for tax reasons. Also I would imagine if the US legalized it, and the ship was registered in the US, most ports would still have a problem with it. They would likely not allow allow the ship into their waters and would require you to stay 10 miles away for carrying illegal substances.
11 cruises in 2012, 90 nights at sea visiting 15 countries
8 cruises in 2013, 56 nights at sea visiting 7 countries
Next cruise: None scheduled
PM me if you need a cruisemate for any Europe, transatlantic, or Panama Canal cruises
Date, ship, cost pp