From a legal standpoint in many states, a BAC of 0.08 is considered too intoxicated to drive, but many here would probably contend that that blood alcohol level does not reach to the point of intoxication. Again, it's a complete judgment call, and the person assuming judgment is the one who's ability to objectively judge is impaired by the time he reaches that boundary.
If drinking is condoned by these Christians, what about marijuana use, assuming it is made legal in a jurisdiction? Will these Christians also say that using marijuana "in moderation" is not sinful? How about Cocaine? Crack? Speed? Everyone has his justification with this leaven.
The Bible speaks of "drunken" but also of an exceeding state of that: 1 Samuel 25:36 "And Abigail came to Nabal; and, behold, he held a feast in his house, like the feast of a king; and Nabal's heart was merry within him, for he was very drunken" The "very drunken" state is most obvious, but drunken might not be quite as readily observable.