TSA's airport checkpoints exist not only to prevent passengers from carrying dangerous items onto airplanes, but also to check everyone who passes for anything that might indicate any wrongdoing. It's a fishing expedition; a dragnet. They freely admit this, though they won't use those words ("if we see something we think might be illegal, we have to do something about it, so we'll contact law enforcement").

They could find controlled substances, stolen credit cards, large sums of cash, or pictures of naked 17.5-year-olds in a wallet. Do you think they're going to pass up that opportunity just to get on with searching other people for dangerous items?

Remember, it's not just about safety, it's about stopping and searching all the good people in hopes of finding the few bad ones. TSA staff are proud of this wholly un-Constitutional practice.