Consider that one of the countries the US recently has been occupying - Afghanistan - is one of the largest sources of opium poppies in the world, and hence heroin,
despite the years of US military presence and massive amounts of money invested into trying to reduce it. Supposedly heroin output
In other words: The US army is wholly insufficient to prevent heroin production in even a single country. And if they were to succeed, they'd just have made production vastly more profitable, and hence attractive, for people elsewhere.
> Then what does stop you from asking this simple question: why don't we fight for more life quality for everybody?
Why do you think this would improve life quality for anyone?
Have you known any high functioning heroin addicts?
Chances are you have even if you think you don't, but just don't know it. I have known at least one - it took a year of dealing with this person regularly before we noticed, and then only because the war on drugs causes massive price instability. Suddenly he had problems getting money enough for his abuse, and ended up stealing some. Until then, he'd been able to hide his abuse for years from everyone including his closest family. Luckily for him, he got it together enough to check himself into treatment before he got into further
The heroin users you see on the street is not nearly all of the heroin users out there, by far, any more than the alcoholics you see on the street are all alcohol users. Even heroin is not so addictive that everyone who use it even have a strong dependency on it; you find recreational heroin users out there. Of those that are dependent, not nearly everyone have problems managing their daily life in ways that makes it likely for people around them to have any idea they are using.
A huge part of the problem with even drugs that can be as nasty as heroin can be is the criminalisation that makes it impossible for users to get properly manufactured doses of known strength at a predictable low price. Most of the nastiest side effect of even many of the really hard drugs are legal and/or problems related to impurities and unpredictable doses rather than actual medical problems related to the drug itself with "normal" use. There are a few drugs where extensive abuse does have nasty medical side effects, yes. But so does alcohol and nicotine - do you propose we use military means to stop all manufacture of those too (if you do, I suggest you look up prohibition to see how that worked out last time)
Want to fight to improve life quality? Legalise pretty much everything, and invest the money currently spent on fighting it into enforcement of strict quality standards, regulating manufacturing and sale, and providing far more treatment and support for those who do need it.
The war on drugs has nothing to do with making things better - it is a mix of religiously founded moralism and a war on the poor (and by extension, in the US it is a war on black people).