alrs was probably in no real danger, but why should they be expected to memorize the exact risk profile of every mechanism they're exposed to? In practice we delegate most risk management to government regulation. It would be very time consuming to evaluate everything on a case by case basis. It's a reasonable heuristic to assume things are safe when they act as they usually do and dangerous when they act differently. Weird behavior is a sign that the regulations might have failed, and weird behavior is by definition rare, so the cost of avoiding it is likely lower than the cost of calculating the true danger.