Although restrictions on liquids have become a fact of life for airlines and travelers, it’s difficult to know if these measures are deterring attacks.
“The trouble with terrorism is it’s not like safety,” said Kenneth Button, a professor at George Mason University’s School of Public Policy. “Safety is a technical problem.”
If some part of an airplane is malfunctioning, it can be repaired, Button said, but averting terrorism is not that simple. “Every time you stop one attempt, they change tactics,” he said.
Security measures such as the TSA’s ban on liquids are partly cosmetic, according to Button. They keep travelers aware of dangers and encourage them to be vigilant, but they also serve to make people generally more confident about flying. - from a Reuters story looking bag on the year-old liquid ban