I mean, different human beings have different capacities to overcome various things. I don't really think that the few recovered addicts out there speak for the whole.
You can expose 5 soldiers to the same fucked up shit and there will be that one guy who isn't as impacted compared to the other 4 who need PTSD management for varying lengths of time.
You also have to consider what they're going back to. I somehow doubt that most drug addicts don't live in an environment that makes it challenging to fall back into old habits.
And maybe you're right, maybe some of them just want that life. Even if they do, it's kind of the implicit nature of a society to keep them alive despite their best efforts.
Unless we're going to write off anyone with a preventable issue, I fail to see many better solutions, because you're just arbitrarily giving a pass to specific preventable conditions.
Our current "solutions" are failing and I haven't seen evidence that refusing treatment would better society in any way. There are repercussions to letting people die off like flies that go beyond just that individual.