I don't do any moral judgement at all, and I also don't predict the future.
I respond to "You are not causing more water to be used by asking a human to work on something.", because that statement is false. (Mental) work has an effect on the human metabolism.
There are projects where long term addicts are given pure medical heroin (Diamorphin) in a controlled environment, and they do considerably better than their control group who does not receive their drugs like that.
100%. I don't want to know how the sausage was made. It's similar to research papers, or history books, where the way we arrive at results or outcomes in the real world is often quite different from the way it's presented in the final form.