Even after the third time, I still can't understand the second sentence. Is it missing some words?
Accomplishment is often defined as the betterment of the world or the future. However, if each individual's life in meaningless in of itself and only derives meaning from the betterment of other aspects of humanity, than the sum totality of humanities purpose and accomplishment is zero. The same goes for betterment of the future, as your life can't have purpose by bettering something that also doesn't or won't have purpose. Hence, the same is being accomplished by everything existing that would be accomplished by nothing existing. Absent an outside or otherwise necessity, existence has no greater total purpose and accomplishment over nonexistence. From an atheist prospective, this is a compelling non subjective argument for the merit of not being born. (By extension, this is also the reason why morals can't exist outside religion.)