Here's a recent idea I had: A tattoo that responds to blood alcohol content over a certain level (e.g. causing an itchy sensation in the skin, or releasing a small amount of something that causes nausea), making it difficult / anti-habit-forming to get drunk. I'm thinking this could solve the alcoholism problem, comprehensively, without discouraging moderate drinking or relying on willpower.

Another variant would rely on social pressure. Although that is less reliable, it could be safer or easier to implement than one that creates a physiological reaction. For this version, one would have a tattoo that is usually invisible, but becomes visible in the presence of high alcohol level. It could e.g. spell "drunk" across the person's forehead.

Of course, such an invention is not quite on par with flush toilets. Not everyone gets drunk, and it is not infectious. Alcohol is not necessary for civilization. However, comprehensively eliminating alcohol overconsumption would be pretty darned helpful and would eliminate a lot of spillover costs of alcohol consumption, like drunk driving, spousal abuse, and so forth. Moreover, ethanol in excessive doses damages the liver, heart, and skin over time.

In addition to helping people who are alcoholics or at-risk directly, a side effect of such an invention is that people who do not drink due to perceived risk of alcoholism (or reluctance to expose oneself to such a risk) would be able to start drinking. This would probably have benefits that go beyond the extra hedons. Assuming it functions as a nootropic for social characteristics, it could lead to more people being better connected socially (i.e. having more close friends).

Incidentally, I don't see a reason something along these lines could not have been developed 50+ years ago.