Are TSA checkpoints worth the expense?

Kriston Capps reports: "Using the same formula* as the researchers (and some similar assumptions), I estimated the same costs for airport pre-boarding security. TSA checkpoints have an annual cost per life saved of $667,000,000—two-thirds of one billion dollars."

Why does the government require screenings if the cost per life saved is so high?

Can you think of other policies the government could impose that would save lives at a lower cost? Why doesn't the government impose those policies?