I have never smoked in my life, and I don't plan to, but did you just put people that are high in the same bucket as drunks and insane people? They are very different types of people.
Marijuana isn't the only drug that gets you high. He was using "high" in the sense of other, more harmful drugs that completely distort your reality and can cause you to become violent. Remember the bath salt incidents a while back?
Getting high isn't just limited to smoking marijuana... There are a huge array of substances that could cause safety concerns for passengers on an airplane.
"high" doesn't imply only marijuana. I would prefer to not be on the same airplane as someone who's just consumed a large amount of methamphetamines, or LSD, or cocaine.
I mean it generally, high as in "people who can't control their behavior due to recent drug use". If you know someone who just ingested "a bunch" of LSD, should that person be on an airplane for 8 hours? Can they control their behavior and not be a nuisance to others or difficult for staff to give instructions to?
I'll point out that someone who is high on marijuana could be a potential hazard during an incident, although may be less likely to cause one themselves.