Marijuana is stupid you shouldn't smoke it, its addictive. Everybody on this board is addicted to marijuana, look at you all most even smoke it every day.[/sarcasm]

If you can afford to and have enough control to do coke only on the weekends then why not? It's cardiotoxic, but occassional use shouldn't be too bad for your heart.
Another example, I love ecstasy over most anything else in the world but I would only do it at the most frequent rate of once every two weeks, usually waiting months in between rolls. I have been able to hold pills for weeks without breaking down and taking them until planned. Why? Because I have a lot of respect for this substance, frequent use would only ruin the experience.

If somebody has respect for cocaine and can live their life doing it on weekends and not needing it any other time, I don't see a problem, and it certainly is possible.

"One possible measure of addictiveness is the degree to which use continues after initial experimentation. High continued use rates do not necessarily suggest addiction; if people who consume a good find they like it and therefore consume it frequently, the continued use rate is high even if there is no addiction. But addiction does not imply high continued use rate, and this has been used frequently as a measure of addiction."

"The fact that continued use rates for marijuana, which is not regarded as physically addictive, are similar to those for crack, which is regarded as highly addictive, also challenges the more extreme claims about addictiveness of drugs. Likewise, the continued use rates for other legal goods (e.g., chocolate, caffeine) are perhaps even higher."
-Jeffrey Miron, Drug War Crimes: The Consequences of Prohibition