Alcohol only arose after the Atlantean epoch to help men to become individualized. It closes man off from his higher capacities and encloses him in himself.
But now all civilized people have reached that stage so that alcohol is an unnecessary evil today. Through its use one loses the ability to get along with others and to understand them. Alcohol is especially harmful for esoterics since its use changes all developed higher forces into forces of the personal ego, repeatedly locks it into itself.
By consuming alcohol one prepares a fertile soil for hosts of spiritual beings, just as a dirty room gets filled with flies.
Source: Rudolf Steiner – GA 266 – From the Contents of Esoteric Classes: Esoteric Lesson – Stuttgart, 8-13-1908