There are actually two separate issues there -- 1) physical allergy or compulsion and 2) mental-emotional obsession -- and maybe this will help sort them a bit:

Some people are physically allergic to strawberries and others are not, but the fact that strawberries can cause physical symptoms for some people does not make an allergy to strawberries into a disease. Similarly, some people lose all control over how much they drink while drinking because they have a physical allergy to alcohol, but that does not mean their out-of-control drinking is caused by a disease. Rather, their bodies simply cannot process alcohol normally just like the bodies of certain other people cannot process strawberries normally.

At that point, the question becomes related to the matter of why people who are physically unable to control their drinking ever drink at all...and again, there is no disease involved. Some alcoholics refuse to believe control over their drinking is impossible, but there is no disease behind that refusal to admit and accept the fact of an allergic reaction making controlled drinking impossible.