To make a difference, we've got to get drugs off the black market. To protect people's health. Drugs available on the black market are of unknown purity. Injecting brings with it special risks, in particular overdose and the transmission of diseases like HIV and Hepatitis C from unsafe injecting practices. To cut the profits of the drug bosses.
Current conditions make it extremely profitable for organised crime to deal in drugs.
So long as drugs are only obtainable from black market sources, drug crime will continue to flourish. To reduce police corruption. As the current NSW Police Royal Commission has demonstrated, police officers have been accepting bribes from drug dealers, and probably have been doing so for a long time. There will always be pressure on young police to accept bribes so long as black market conditions exist. To reduce property crime.