The banning of anything, whether it be booze or books, is rarely an effective measure at stopping people from partaking in it. If anything, it suggests to people that there's something special about the thing being banned and only serves to worsen the problem.
If you want to stop alcohol abuse, you're much better off educating people rather than taking the lazy man's route and simply banning it. (which is what you said i think)
Are the people for legalisation basically into reversed-phsychology? And hoping people get bored with drugs?