Yes, you accept that some people are going to be addicted to drugs, just like they are now. There's nothing else you can do. We can try to help them whenever, but that's easier to do when their addiction isn't illegal. For instance, I watched an episode of a show called "Intervention", where a girl was addicted to heroin or some similar drug. The intervention actually worked, probably because she'd hit rock bottom. She stayed in treatment until she was clean, and stayed clean even after treatment for a couple months before she was picked up for a couple of warrants from things she had done before she got clean. She went to jail and when she came out, she was right back on drugs.
With a more understanding view of the situation, she might not have gone to jail and might still be clean. Just because people want everyone to have the legal right to do drugs doesn't mean everyone is just going to condone their use and accept addiction and the crime that goes with it. What it means is that we can deal with it better.