And I honestly don't see how a safe injection site would help with any of that unless the users kick their habit.
Do you honestly not see how safe injection sites are a step in kicking their habit? They are starting to care about their well-being enough to get help, so maybe they will start thinking about how to get off drugs.
The sites are also about more than just drugs. They're help centers for anyone that needs help. If they're the one being abused, they can find crises centers and shelters, and if they are the ones abusing, they can find counselling and such. They can also look for ways to find employment or education that will lead to employment. Basically, everything they need to turn their lives around when they make the desicion to do so. Sites have already been in place in Europe for a while, and the results have shown drastic improvement.
In addition to health benefits, approximately 45 sites in a dozen cities in Europe and Australia are credited with limiting violence associated with drug use, reducing the public nuisance of people injecting on the street and the health risk of needles discarded in public places. source
It is their fault.
Users will sometimes be used to a specific purity of the drug that their body can handle, then without knowing it will receive a much stronger purity that will kill them. It's like (for lack of a better analogy) someone who goes cliff jumping without realizing there is rocks right underneath them. Sure, it was dumb, but it doesn't mean they deserved to die.