Prohibition of alcohol didn't work in the 20's. Only violence resulted from prohibition. Drugs are the same. We also can't punish people for possessing a certain substance-- if anything, we should influence drug rehabilitation programs rather than keeping it illegal.
If it's legal, it can be regulated. Putting people in drug rehab centers also is more effective than throwing then in jail.
There's a difference between legalizing marijuana and legalizing all drugs.
Marijuana yes, and tax the crap out of it. Cocaine, heroin, crack, etc. No.
Many drugs are poisonous, especially medical ones (because they affect the body). Drugs can be very dangerous, they should be made illegal if they are too dangerous. The problem with marijuana is that it was never very dangerous (a lot less than alcohol). It seems they forbade it mostly to make sure it would never get popular/normal like alcohol.
Why would you do drugs?
Drugs are a huge reason for a lot of crime that happens all over the world. Legalizing these harsh drugs (crack, heroin, cocaine) would only make these occurrences happen more often. Granted they would be easier to get so there would be a lot less "drug deals gone wrong" on the news. But the how much a person could obtain at one time will rise. Now instead of seeing someone shot over a drug deal you start seeing plenty more overdose headlines and also, If they are legalized how much easier would it be for our youth to get a hold of these drugs.