I don't really drink, but a generous explanation might be the "edge" of living under capitalism. Sometimes religion is the opiate of the masses, sometimes it's alcohol. And sometimes it's just opiates

addiction is a motherfucker; once you're trained, and the initial training can be completely accidental or out of your hands in a tangible way, sobriety is something that requires discipline to maintain, the reward parts of your brain want more. ex smokers want the anxiety relief, alcoholics want to exist in that state because they feel more themselves in it now. It's especially hard if your addiction is socially acceptable. Alcoholics and nicotine addicts have to stare at their addictions every time they shop, go to a gas station, and in quite a lot of social situations. and quite often the brain, especially for the first few years, loves to invent reasons to relapse on sight/perception of the favored drug use, and logic and "good sense" are present all the way up to the point of use, telling you not to and it's happening anyway because addictions circumvent the rational. It's seriously just pure will for a while, and most people just do not have that in sufficient quantity.

the specific rationale will be different for everyone with the problem, but "taking the edge off" is implicate in the problem; their brain is screeching that they're not okay, not normal, and [thing] would fix it. That's all it is. It's sad. It really sucks to be around addicts of any type who are not in control, but... I really don't think of it as excuse - that person sincerely believes they need it and their brain is fully complicit in an unconscious and overpowering way.