It's strange, how it's almost always the same voices that decry the "Destructive Alcohol Culture" allegedly pervading the Forces, are the same voices that espouse relaxation of the rules governing illegal drug use. Coincidence?
Aside from the effects of illegal drugs (the whole reason for them BEING illegal!), one cannot partake of them without commiting a serious offence - this alone is sufficient to maintain the strict standards that the Service(s) apply. For this reason, if no other, the perennial "Alcohol vs Drugs" argument is void IMHO.