I just caught this on twitter. Seems that his sponsors don't think its such a big deal.
Tax laws and drug laws and sex laws are for the humble servants of the state, not for the noble people who dedicate themselves to our own good. They have to work so hard that we must not fault them for acts the stress of hard work drives them to. It is really nerve-racking deciding how much to pay yourself.
Big central government just needs one more chance. Really. Trust them. We know more (not less) government is the answer and we just need to keep making it bigger and more centralized until we get it right. We workers just aren't working hard enough for the common good. We must do more.
Phelps is some kind of a shirker, having fun when he should be working to stop gorebull warming or being a role model or doing something else for the common good. He isn't being properly grateful to society for all that it has given him.
/sarc
It is one thing to ban substances in sport that actually aid athletes performances. Sports have rules, and this is just one element of the rules. If the drug both provides a improved performance and is very harmful to the athlete, then governing bodies might want it to be possible to be good at the sport without also bringing on premature death. (On the other hand, at least in some sports we accept similar tradeoffs without drugs without much controversy. Apparently the life expectancy of retired NFL players is about 20 years less than the general population, simply because of the immense physical toll that games puts on the body. And I can't imagine the life expectancy of retired boxers is that great either, although I don't have stats).
Enforcement may be so difficult that such rules might be impossible to enforce and the sport become a joke as a consequence (see cycling) but philosophically this can at least make sense.
However, the actions of the IOC (and the World Anti-Doping Agency, which is a creation of the IOC) to ban recreational drugs as well simply co-opts world sport into the huge, stupid, bureaucratic and venal "war on drugs". The decision of other non-Olympic sports to allow the IOC to do the running on this is just desperately dumb, too. It means lots of bureaucratic stupidity, and a very War On Drugs style list of "evil" drugs, when the question of "What drugs should be prohibited" should clearly vary between sports that require different skills and have different cultures.