Your analogy is very poor. You are allowed to fire your gun under legitimate circumstances only, such as target practice, hunting, self-defence.
You can kill someone with a car, or a knife, or a cricket bat, or even a pencil. The law does not stop you from buying or possessing such articles, it prevents you from using them in the wrong way.
You are allowed to purchase and consume alcohol as long as your doing so does not cause you to become a danger to others or to yourself. There are different levels of intoxication, but for a normal person a couple of units consumed should not make you 'intoxicated'. If in your case it does, or you don't know your limit, then you should probably avoid alcohol totally.