Originally Posted by Bart

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When you enter a checkpoint, you do so voluntarily. Actually, it's an agreement you've made as a condition for flying a commercial airliner. If you do not successfully complete the screening process, then you don't fly. It's as simple as that.
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TSA was originally created to screen all modes of transportation. This should not be a surprise to you. However, the priority, clearly during the aftermath of 9/11, was with airport security screening. Again, this should not be a surprise. Eventually, TSA is supposed to establish screening methodologies for other modes of transportation or at least address security issues.