It's been illegal to carry an intoxicated person for as long as I can remember. It's strange how the industry has always plied their customers with liberal quantities of alcohol.
The thing about getting drunk is the feeling that 'It'll be okay to have another', once the first drink or two have been consumed. The only sure way to avoid situations like this is to have a maximum legal level of blood alcohol for passengers as well as aircrew. Somehow, I just don't see this happening.