This is an interesting question, and takes a bit to unpack.
It appears that our ancestors have been consuming alcohol for something on the order of at least 10 million years, concurrent with the separation of the genus Australopithecus— the precursor of hominids— from the genus Pan, which includes chimpanzees, bonobos, and gorillas. Interestingly, other more distant members of our extended family tree— orangutans and baboons— have no ability to digest alcohol, so they don’t consume it.
So there must be either, A) some evolutionary advantage to alcohol consumption, B) something faulty with your assumption that alcohol makes us weaker, or C) both.
Of course the answer is C. There is a distinct evolutionary advantage to being able to use a food resource that other animals can’t consume, which in this case could be the fermented fruit that contained the alcohol which was consumed by those early ancestors. Similarly, there must be no notable evolutionary disadvantage to the consumption of alcohol significant enough to effect the survival and reproduction of the species, else such a disadvantage would be evident in the course of 10 million years of evolution.
While it may meet some arbitrary definition of the word “weaker” that you may apply, it doesn’t seem to negatively effect the survival of the species, and in fact, there may be benefits to it, as evident in the fact that we have retained the ability to metabolize alcohol over these 10 million or more years.
There may be negative short-term effects on individuals immediately concurrent with alcohol consumption, and there are certainly negative long-term effects on individuals who consume alcohol in excess, but those negative effects have not manifested themselves in the evolution and survival of multiple species of apes—including us. Essentially, it has not negatively affected our ability to feed ourselves, reproduce, care for offspring, and pass our genes to subsequent generations. And as it turns out, that would be the only definition of “weaker” that applies in evolution.
The featured image for this article is “Scene of a Banquet, Herculanum Fresco”.