I don't consume any drugs other than alcohol and don't have any interest in doing so, but if I did, it would be trivial to obtain them in my (smallish) city. Everyone knows where to go.
So illegalization doesn't meet its purpose (making drugs difficult to get) and yet it does have negative effects (the drugs sold have no quality control at all -which often causes deaths-, pay no taxes, are sold without any legal warranty, etc.) I'd rather they were sold in pharmacies, being dispensed together with reliable information (like tobacco), forbidden to minors (which could actually work reasonably well, because no one would go to the trouble of setting a black market exclusively to sell to minors) and paying taxes that could be used to fix the problems they cause.
To me, this is enough grounds for legalization, regardless of the exact health effects of drugs.