He was in too much of a hurry to take the time to handle his gun in a responsible manner appears to be his excuse.
It sounds like he should lose his ability to carry a gun on a plane for a while and go through some basic gun handling classes where simple safety procedures are drilled into him over and over again.
An this should be his only warning. Next time, fire him.
You see nothing wrong with these rules?
They seem designed to enable incidents like this.
Better solution. Fire the TSA/HS bureaucrat who came up with the rules. No second chance.