Apparently, Phelps believes he's above the law now that he's won 14 gold medals. He is not, and the state of South Carolina should prosecute him to the fullest extent under the penal code.
Clearly, this is not some isolated incident - he was caught using some sort of advanced apparatus to ingest the marijuana. Looking at the photo, it's indisputable that he knows what he's doing, with one hand expertly placed on the carb to extract the maximum amount of smoke.
Some will argue that at 23 he deserves forgiveness, especially in light of his dedication to his craft and the glory he's brought to his country. I believe it's just the opposite: The shame for this evil act is in direct proportion to his achievements - which incidentally he has now completely nullified.
Phelps is nothing but a common criminal. Only a stint at a maximum security prison will cure him of his hubris and immorality.