I’d rather have a professional take care of business, too. But over the last 20 years we’ve seen example after example of flight crews and passengers handling things (even with armed highjack attempts). And the number of FAMs arrested for felonies has FAR outpaced the number of arrests BY FAMs.
It just doesn’t make sense to spend a billion dollars a year on the off chance that the FAMs happen to be on a flight where there is a bad guy who is (1) too diabolical to be stopped by crew or passengers and (2) not diabolical enough to use the FAMs’ guns for evil.