Speaking as someone who definitely doesn't want alcohol banned, this is kind of a specious argument. Bad-for-you-X is not banned therefore bad-for-you-Y should

Speaking as someone who definitely doesn't want alcohol banned, this is kind of a specious argument. Bad-for-you-X is not banned therefore bad-for-you-Y should not be banned either, is not really sensible. A better argument, should you wish to produce one, is to describe the societal benefit you get that offsets the potential negative consequences. Or perhaps you can explain how banning does not produce the desired societal effect in the first place (I'm visiting Canada at the moment and it's amusing how legalisation of cannabis seems to have led to a dramatically reduced availability...) I think these kinds of arguments are going to be more effective in getting your message across.