It's set by people for whom the clock serves as a mechanism to garner alarmist attention whenever they feel short of it. In so doing, they diminish not just themselves, but science as a whole.

At best, the clock is indeed a measuring device; one not of our peril, but of the anxieties of a group of otherwise non-notables. In that sense, it figures that it'd say we're closer to "doom" than during the Cuban missile crisis, because that's the intensity of current vibes, particularly if you're a modern activist plugged into the techno-socious of reactionary negativism.