I'm autistic, so I don't know if this applies with adhd, but for me it's not a choice (sensory processing disorder means, for me anyway, not being able to not be alert and aware of literally everything going on around me), and if it was, it wouldn't be about "warding off harm" in some abstract way, it's more about trying to be prepared for every possible outcome, because being caught unprepared would cause even more anxiety..
Aren't brains fun? π