<<you avoided answering the question about setting an example to youth.>>
It's not an easy question to answer.
Doing coke as a youth, he wasn't a public figure and he wasn't able to serve as an example to anyone. If anything, I think his youthful use of coke would set an example to some people with similar pasts that youthful cocaine use is not a bar to seeking the highest office in the land. They would be enabled and empowered to be the best they can be, rather than giving up on themselves, thanks to Obama's example.
OTOH, you apparently fear that some young people would be enticed into cocaine use by the example of Obama. I find that highly dubious - - personally I never met anyone who used coke because they thought that some politician did. People use coke (IMHO) to have fun, not to emulate some politician. I think rock stars and film stars can be more effective "salesmen" for coke than politicians, but even there, in the end, it's always a personal decision of an individual, to snort or not to snort.
In any event, Mr. Independence & Self-Reliance, what about individual responsibility for one's actions? Assuming that using coke on balance has a negative overall effect on the nation rather than a positive (which I'm certainly not prepared to concede) people are free to decide for themselves and must bear themselves the responsibility for their decisions.
Would you be as condemnatory if the substance were alcohol rather than dope? This "setting an example for the youth" doesn't go very far, IMHO, if it starts to impinge on the way I, or Obama, or anyone else, wants to live his life.