Simon: the ex ante probability of failure of the LHC is independent of whether or not if it turned on it would destroy Earth.
But—if the LHC was Earth-fatal—the probability of observing a world in which the LHC was brought fully online would be zero.
(Applying anthropic reasoning here probably makes more sense if you assume MWI, though I suspect there are other big-world cosmologies where the logic could also work.)
Simon: the ex ante probability of failure of the LHC is independent of whether or not if it turned on it would destroy Earth.
But—if the LHC was Earth-fatal—the probability of observing a world in which the LHC was brought fully online would be zero.
(Applying anthropic reasoning here probably makes more sense if you assume MWI, though I suspect there are other big-world cosmologies where the logic could also work.)