You discount feedback effects

There are feedback effects with substance addiction (and other behaviors too such as gambling).

It is true that many take up drinking or other drugs because of life issues; and only a fool could deny it.

However, even when that explains the start, it cannot be taken as answer once feedbacks are in place. You might lose your job and start drinking, but if you want to get a new job you have to quit drinking first, or you'll be fired after showing up drunk, and that's supposing you passed the interviews drunk. You might enter a personal economic slump and start drinking, but you can't start paying off an increased debt unless you first quit drinking so it stops eating at your budgets. You might have family problems and start drinking, but your wife or kids will not love you again if you're intoxicated most of the time they need you. And so on and so forth. Alcohol, sure enough, numbs the pain, but constant or high-peaking use (which can lead to addiction) increase the problems whose pain you were numbing in the first place, so you need to deal with that artificial increase - by quitting.

This is why alcohol (and others, but most certainly not tobacco and probably not marijuana either) is so destructive. Tobacco, even at the height of addiction, does not become a life altering burden unless and until, many years later, it triggers disease. Legality might help minimize the social effects of tobacco (at least for now, as I foresee tobacco becoming illegal in the West within my lifetime), but it still remains true that the nicotine dosage is low enough to not cause any of the short term disruptive effects. Alcohol (and some others) are different because they cause life altering effects even in the short term, through both mind-numbing intoxication and fast falls into these feedback cycles. You underestimate them at your peril.

(I am not saying that GL_in_lyrics underestimates them, though, as his post seems to have reasoned out that he isn't hurting anyone apart from himself even were he to become an alcoholic. I am only saying that you do.)