This is also generally true of hard drugs like heroin and cocaine, but here I think the addictive qualities are what makes them a social problem.
What do you think happens if you take a low dose of marijuana or mushrooms?
You are stipulating that ethanol [0] is the only psychoactive substance which can be properly dosed for its effects? Sorry, but you realize that's rather.. uneducated? It's about potency, tolerance, bio-compatibility and the resulting individual threshold.
Case in point: Your "one or two" drinks could be beer, booze shots, cocktails, wine and many other products with varying, often not even labeled, potency. You could drink them over the course of 2 hours or 5 minutes, all of that influences the final effects, especially how regularly you are having your "only one or two drinks".
That's why there are such things as "functioning alcoholics" or people who regularly consume high potency cannabis and thus don't even notice any effects when consuming low potency cannabis.
Your anecdata is incorrect. I can smoke two bowls (or even two 1/8ths) in the course of say 45 minutes, and I will more sober than if I had two IIPAs or two shots of tequila.
https://www.webmd.com/mental-health/addiction/news/20101101/...
Alcohol ranks very highly because of it's severe harmful effects on the body. However, behavioral effects tend to be those which make drug users a threat to society.
But cocaine's harm is highly dependent on its form. In some pre-Colombian civilizations, as well as in some parts of modern Colombia and Peru, drinking coca tea is/was quite common, and yet life carries on without serious problems. However, smoked and snorted cocaine tend to cause severe behavioral problems in a subset of users, and high doses of cocaine can cause heart attacks. Legalizing coca leaf/tea is an approach I've toyed with to significantly reduce the profit margin of drug trafficking (hopefully) without increasing the use parenteral cocaine too much.