Got to agree with verticalspin here. It's not about knowing when someone is over the limit for driving. The wording says, "...appears to be intoxicated." So what's "intoxicated" mean? Overly-boisterous, disruptive behavior? The passenger freely admitting that he had a number of drinks ("liquid courage") prior to the flight?
If the FAA wanted to, they could be violating pilots all the time for allowing people who "appear to be intoxicated" onboard their aircraft. Last job I had, my boss was "under the influence" more often than not. Let's be honest, in the corporate world, if pilots stopped allowing drunk people on their aircraft, there would be very little flying done. That's an exaggeration, of course, but anyone who's ever flown corporate (or charters!) knows what I'm talking about. As long as nothing happens and nobody dies...
Ah, but there's the rub. In this case people did die. And maybe it was caused by the (admittedly) drunk guy who's seat belt or harness tether or whatever got tangled under the throttle and pulled it back when he sat up. Maybe the NTSB will trace the chain of events of the accident back, and focus on allowing the "drunk" guy and decide to go after the pilot and/or the operator this time.
Would you?