"When you have someone like you or me who doesn't intend to attack a flight, whether we have a Swiss Army knife in our pocket or not doesn't make any difference," said Ron, president of Virginia-based New Age Security Solutions and former head of security of Ben-Gurion Airport near Tel Aviv, Israel.
"If you have somebody like one of the terrorists (who was involved in the 9/11 attacks) or a terrorist who is still out there, I'm not sure we'd want him to have even a Swiss Army knife," Ron said.
"Risk is not measured by the item, whether it is a knife or gun. It is measured by the person holding it. A bad guy with a Swiss Army knife can still cause a lot of damage to the crew and passengers in the cabin before the aircraft can land."
That potential for violence is part of what has flight attendants concerned.
Former flight attendant Tiffany Hawk is "stupefied" by the move, "especially since the process that turns checkpoints into maddening logjams -- removing shoes, liquids and computers -- remains unchanged," she wrote in an opinion column for CNN.
And Veda Shook, president of the Association of Flight Attendants, said the move is "completely unnecessary" and "makes no sense." Rather than freeing up time, she predicted that security officers will get more bogged down testing and measuring the knives to see if they meet the criteria.
The Flight Attendants Union Coalition, representing nearly 90,000 flight attendants, and the Coalition of Airline Pilots Associations, which represents 22,000 airline pilots, also oppose the rule change.
By Monday afternoon, more than 20,000 people had signed a petition to WhiteHouse.gov calling on the TSA to keep knives off of planes.
Traveler Emma Siemasko, a writer and blogger in Boston, sees "the flip-floppiness" of the TSA's policies as the real problem. "There are too many rules to follow and there also doesn't seem to be much rhyme or reason."
Many travelers see rules that haven't been eased as bigger hurdles to the air travel experience: "I would prefer they get rid of the liquid restrictions. I'll leave my penknife at home," wrote a CNN reader. "But trying to find 3 oz bottles of everything and stuff them all into a quart baggie is a royal pain."