For an insight into what may be at the very root of these problems, this is an interesting article.
http://www.gaps.me/?page_id=20While it deals more with depression and such disorders she does mention how such people end up being more prone so substance abuse. The link between psychological disorders and addictions is not exactly a revelation.
Wat, while people may choose to have that first whatever, as FNM has already stated, no-one actually chooses to go down the path of self destruction.
When people have an attitude that you can choose just to quit whenever you want and therefore implying, or sometimes saying, that you are somehow weak or inferior because you cant stop, all you are doing is making it hard for these people to even acknowledge their problem.
Could you imagine how hard it would be for someone trying to face up to such a problem, knowing, or thinking, those around them will judge them because they cant just stop at will?