Originally Posted by
Often1
The security issue is non-existent. That happened back in 2003 when TSA implemented screening of all checked luggage. The security issue is now a matter of carrier policy. All of this presumes that the inividual had checked luggage, something which is ever more rare.
As to opening a flight, while it is the Captain's discretion and he may certainly do so if he wishes, the crew would generally try to talk a rational passenger with no major issue, out of it. But, Captains tend to err on the side of caution. Having a distraught passenger at FL 40 is no fun and if someone is belligerent about it, the Captain wants them gone in any event.
All of this presumes that the effort caused a delay. The issue for consideration is the length of the delay into the destination, not the delay in departure. You will sometimes see a bit more of a lackadaisical approach to schedule when there are other delays which will occur no matter what.
Even without a checked bag, someone who deplanes might deliberately leave something behind on the aircraft. Carry on items are supposed to have been screened too, but that doesn't mean that TSA doesn't frequently miss things.