>>1
The standard rhetorical move when you're trying to overturn an opinion that's accepted as obvious and eternal is to place that opinion in a historical context.
For example: opium used to be considered a "nasty habit" rather than a horrifically addictive and illegal and horrible drug. It was outlawed mostly to put pressure on the Chinese population that was the primary consumer of it. Marijuana was actually included in the U.S. Pharmacopeia until 1945 or so, recommended for treating nausea and minor pains; it was legal and commonly used while alcohol was still illegal during prohibition! Amphetamines used to be used as an over-the-counter decongestant, for christ's sake. The list goes on; virtually every drug that is illegal today had some level of social tolerance or medical use at some point. Pick your drug, place it in a historical context and trace out the linguistic and social history of it. Point out that the legal status of these drugs isn't some divine writ, but a social and political construct.
Question the assumptions behind the language used to describe the drugs; every word like "intoxication", "dope fiend", "addict", "junkie" has a history and a context and is an argument: a specific attempt to frame the debate.
Come back to the point of what these drugs actually DO to people. Is there really no medical use? Is the effect the same as or worse than alcohol, or caffiene, or nicotine? What social context does the illegal status force on the drug, making the terms you're questioning a self-fulfilling prophecy?
If you really dig deep on your research, you can fill up an hour of speechifying really easy.