Likely to be a hot topic among the anti-s [the pro-s being all too doped up to bother posting!!!]
It should be decriminalised for medical purposes, I think. If it is, I think it would then lead to general legality, since enforcing the legal/illegal distinction would be next to impossible for the overworked cops.
However, I believe on the wider issue, prohibiting anything just puts production, sale and profits underground into the criminal world (look at the only experiment in Prohibition of alcohol in 1920's America). If junkies, or indeed anyone, could get heroin, crack, whatever, on prescription from their GP, to be consumed in controlled circumstances, at a realistic price set by the government, crime rates globally would collapse. Yes there would probably be a few more sad junkies around than there are now, but they wouldn't have to steal for their habit, they wouldn't die from overstrength doses, they wouldn't be outside society, excluded and abandoned. It would also be about as cool as snorting Rennies, which would destroy most of the appeal for the young.