The point of medical heroin, or other harm reduction programs, is to allow people to get on with their actual life without the all consuming addiction being front and centre all the time. I'm currently on a methadone program in the UK (there aren't any heroin based programmes as far as I know here) and it lets me keep up my job as a software engineer without daily worries about having to make sure I can score and not be 'sick' (i.e. withdrawing) and unable to work or go to the office. A heroin prescription would accomplish the same thing for me, and for people in a worse situation - perhaps unemployed or homeless - it would mean even more, since they could devote their energy to rebuilding their life.
Personally, I don't really need a safe injecting space - I own my own home and have a pretty stable lifestyle, but again, I can see how for other addicts it would be incredibly helpful. Again and again, as seen in other comments, it can be seen how despite objections these places provide an objective positive benefit to society.
Heroin addiction is 90% looking for or doing something to get more. It’s an incredible time sink. It’s impossible to have a meaningful life like that.
What medically administered heroin does is allow people to get that time back so they can rebuild their lives. Once they see that things are better, they become more successful when finally coming off of it. Even if it takes forever, they are still productive members or society instead of a drain.
Like 'skellera says in the sibling comment, heroin is an incredible time-sink. The methadone programme I am on (provided free by the UK NHS) is something that will let me gradually reduce the amount of heroin I'm taking, and eventually yes, get clean. After a couple on months in, I'm down to ~25% of what I was taking daily before, and that should reduce further to zero over time.
A methadone maintenance program will gradually increase the amount of methadone prescribed, while the user reduces the amount of heroin they take, until the user is 'stable' and no longer using heroin. After that I certainly would like to then stop taking methadone too, but in some cases the maintenance can continue indefinitely and it would still be considered a net positive outcome...
Personally, I don't really need a safe injecting space - I own my own home and have a pretty stable lifestyle, but again, I can see how for other addicts it would be incredibly helpful. Again and again, as seen in other comments, it can be seen how despite objections these places provide an objective positive benefit to society.