If you think there is more drug-related crime and public heroin injections in "puritan" US cities like Seattle vs European cities like Frankfurt or Amsterdam... you must not travel very much.
Punishment of drug use does nothing to prevent drug use. Its only value, therefore, is sadism.
I support decriminalization on purely moral grounds, but am skeptical this will lead to less (and not more) drug-related crime or public use of hard drugs, based on my anecdotal observations in Europe.