Let's say that an unruly drunken passenger has the same potential to cause major disruption on a flight as the pilot.
Let's say that in an intoxicated and uneducated (re. aircraft systems/flight safety) individual is more likely than the pilot to cause such disruption, given his inebriated state.
Why then should passengers not be held to the same standards of sobriety as the flight crew at boarding, or if that seems a stretch at least held to the standard of blood alcohol legal to drive?
Flag troublemakers at the gate and let them have a blow. Over the limit, no boarding.
Punishment is closing the barn door after the colt has bolted, what say keep the problem at the gate and let the ground staff/airport police handle it.