The only argument that you missed that some people may argue is that their taxes (Especially in Norway where taxes are very high) are now going to helping drug addicts get their next hit for free. Some people don't want that to happen, no matter how much good it does otherwise. The rest of your post is spot-on, it's just important to consider arguments from every side.

I know there are a lot of good responses to this argument ("you'd be paying for a jail cell anyway", "it's a net benefit to society", etc), but you have to remember that there is a very large portion of society that think drug users are inherently terrible people unworthy of help and won't listen to any logic beyond that. Although HN is made up of people who are willing to think through arguments fully and recognize why this program would result in a net-benefit to society (at least, in theory - it hasn't been tested yet), it's important to remember that people exist outside the HN bubble. To these people, the idea of helping someone obtain drugs (especially the government helping someone obtain drugs) is a terrible idea, hard stop.