I’m skeptical that legalization of all drugs would reduce most crime except for crimes related to use and distribution of a controlled substance. Sure, drug dealers would not be killing each other abs any innocent person in their periphery. Legalizing alcohol did not mean that alcohol use/abuse is not responsible for many crimes, especially assault, sexual assault, vehicular homicide, theft, child abuse, all manner of domestic violence, etc.
Legalization ended the bootleggers shooting it out with each other.
And these days alcohol is affordable enough that the wino commits only minor crimes to support his habit. The crackhead sticks people up because he needs a lot more money to support his habit.
Winos only commit minor thefts, sure. But alcoholics or drunks commit many other types of crime: vehicular manslaughter, assault, murder, rape, a variety of domestic assaults. Also a fair amount of white color crime, medical malpractice, etc.
You are right: liquor store owners are not shooting it out in the streets nor are beer distributors. But there is still a lot of crime committed while under the influence of alcohol, including crimes that probably would not happen if alcohol were not a factor.
So, while I am not opposed to legalizing marijuana, I do have some concerns with regards to public safety. As for other drugs: those include everything I've mentioned above plus crimes related to impure or misrepresented drugs being used, etc.
Of course, there is the absolute fact that alcohol abuse leads to many deaths annually, as does drug use/abuse.
I'm not proposing criminalizing alcohol. I'm just pointing out that a lot of crimes are committed by people who are abusing alcohol or under the influence. Those types of crimes with the root cause being drug use will not lessen with legalization and in fact may increase.
The real issue is that we very much need to address mental health issues---and also chronic pain treatment. Both are seriously underfunded, scare, and too often overlooked.