It does harm and affect others though. Depending on the drug & circumstances. But you can't just pretend that heroin users just carry on their lives like normal without negatively affecting anyone else.

Most heroin users with access to cheap medical grade heroin (medical grade heroin is cheap - we know this because it's in use in healthcare; e.g. the UK NHS prescribes it under the generic name diamorphine for a variety of uses, including post-op pain - in hospital only - in some cases) are perfectly able to carry on with their lives - and hold down jobs. With heroin as with most drugs the criminalisation is what is causing most - not all - of the harm.

To repeat the oldest point in the book.. should we ban alcohol too then? Or does that not affect people depending on the circumstances?

No because it isn't as addictive or harmful as other drugs. Yes it depends on the circumstances, but harder drugs are more likely to cause harm.

Yes I know about the David Nutt report. It's not remotely objective.

I draw the line at heroin in my personal usage too, so we're not of completely different minds. By your logic where should the line be drawn then? Genuine question. Is LSD fine? Ritalin? Coke? Meth?

There has to be an option between locking people up if they're trying to destroy their lives and standing around doing nothing - if not actively helping them.

The people wanting to use drugs would view "punished" as anything that gets in the way of them and their drug of choice. Saying it harms no one is to say that the person using isn't being harmed.

I have (though probably used to have more) libertarian sympathies but it seems like that falls down in a large number of hard cases. I don't want to run other people's lives any more then I want someone else to run mine but there's an extreme version of the libertarian argument that equates any help with control.