He wasn't at the controls. He was hitching a ride on a flight piloted by somebody else, which isn't unusual for pilots. You should read the full story, but this is what I understand what I heard earlier.

He was already depressed and had lost somebody close to him recently. Did mushrooms, (presumably) had a bad trip, doesn't sleep for the next 48 hours, then boards the flight as a passenger. Apparently he was suicidal and felt like he was dreaming so he probably didn't have a full sense of the consequences of his actions; I don't think he was out to kill anybody but himself. Told the flight crew "you better get me off this flight or it's going to get bad" or something to that effect after already acting out and needing to be restrained. Then they make an emergency stop to let him off.

I'm for legalizing psychedelics, but unfortunately it seems the mushrooms are integral to the story. Although it should be said that this guy very clearly wasn't in a state to be doing psychedelics without any professional supervision, guidance, and/or aftercare. I've said all that I know about the story here, and it's admittedly very little, but chances are that a little bit of education would have gone a long way to prevent this.