What happens if someone is irresponsible and they drive recklessly, ending up in a rolled over car in a ditch somewhere, trapped. Should society just say "well, they brought that on themselves, fuck 'em"? As a society we've decided that the appropriate thing to do in such situations is to expend collective resources to help them, providing rescue and hospitalization as necessary. Just as when someone recklessly mishandles flammable materials in their home and burns their own house down. Just as when someone decides to commit suicide.

There is a social responsibility to help one another, and we've consistently bought into that responsibility along many fronts, even when individuals get themselves into trouble through their own errors or choices. In the long run it turns out to be a net benefit to society for a lot of reasons, because often times it can put people on the path to turning their behavior around, and often times people make mistakes and learn the error of their ways. Also, addressing social responsibilities earlier (in this case, at the addiction stage) can save money down the road by avoiding the costs of other social responsibilities later (e.g. emergency medical care). But if society doesn't reach out then those people may not get that opportunity to become productive members of society, and they may end up seeing a society that doesn't value them and is adversarial to them, which is an encouragement to reciprocate.