Our pre-vital nonexistence and our posthumous nonexistence are symmetrical, alike in all relevant respects, so any objection to the one would apply to the other.
According to his symmetry argument, it is irrational to object to death, assuming it ends our existence, since we do not find it objectionable that we failed to exist prior to being alive, and the way things were for us while not existing then is just like the way things will be for us after death ends our existence; our pre-vital nonexistence and our posthumous nonexistence are symmetrical, alike in all relevant respects, so that any objection to the one would apply to the other.