From what I saw of the "passion of the christ",I believe Mel Gibson to be a religious fundamentalist. This means to me that his religion becomes a panacea for alcohol excess.
Or to put it this way, religion can be the gateway to addiction.And vice-versa.
The pattern of the Christian "swing" has been established by Jimmy Swaggart and others by preaching the Manichean "good" and lapsing into "backsliding".
This is probably because religion is used as a protective device against destructive behavior. We see this in Bush.
Alcohol addiction is a problem that doesn't require condemnation but understanding. I would prefer to give him credit for admitting a mistake which is not in vogue these days particularly in Washington.