You're correct that addicts won't stop using because of decriminalization, but it does open new ways of helping those people.

Instead of forcing them to hide, prosecuting, incarcerating and labeling them as undesirable members of society, you can create infrastructure and programs that could help many of them deal with their issues over time.

Sometimes the hardest part of exiting addiction is that the only people who understand or tolerate you are other addicts, creating a very hard to escape circle.