I agree with the asymmetry argument for antinatalism. Imagine the best life of the Renaissance era: Being born a prince with wealth, charisma, and brilliance, with the immense additional luck of enlightened and noble parents and suffering no diseases until very old age by 1300's-1500's standards. The fact remains that our hypothetical prince who came into existence then was deprived of all future goods upon his death. He never enjoyed the internet, automobiles, or flight. News and messages in his day traveled slowly, even with a personal army of message runners. A poor person alive today has access to orders of magnitude more entertainment and of greater quality than our prince.
In fairness, however, the prince had temporal power over many other people, especially compared to today. A Renaissance prince was well and truly above the law in ways that even comtemporary billionaries aren't. Upon ceasing to exist, our prince loses that temporal power. The prince is dead and by definition is no longer aware of the loss, but the loss still accrues to the once-living prince. That loss to the prince may be to the gain of the prince's subjects, but the prince wouldn't see it that way. If the prince simply hadn't come into existence, there never would have been a prince to suffer any of these losses. Hence the assymetry of benefits and costs of coming into existence v/s never coming into existence.