Detailed Explanation
Allison's death in the pilot episode is devastating once you understand it. She and Holston discovered evidence that the outside might be survivable—that everything they'd been told was a lie. Allison chose to go outside, expecting to survive. But the suits used for "cleaning" are sabotaged: the visor shows a beautiful landscape while the wearer actually sees the toxic wasteland, then the suit degrades rapidly. Allison was killed by hope itself, and by a system designed to make examples of anyone who questions it.