Thanks for following up. You're asking about a number of issues at once, so let's see if we can distill them out. First, you wonder why people must have "essences" at all. That's a big question -- Hume is a well-known philosopher who can be read at suggesting that persons or selves don't exist. That 'no self'' position is a minority view within philosophy, but is arguably the position espoused by Buddha and has some affinities with the 'eliminative materialism' defended by Paul and Patricia Churchland. I'd encourage you to explore those views further. Second, in my earlier response, the point that we might identify someone on the basis of social facts about him or her was not an argument for genetic facts being essential to a person. Rather, my purpose in making that point is to illustrate how this line of reasoning is invalid: Whether a is F can be reliably determined by whether a is G. Therefore, G is a's essence. To see why, suppose (again) that the way we would normally identify Mandela is by...

I'm pretty confident philosophers do want to make sense of personal identity. But you are taking issue — not unreasonably, in my estimation — with a claim many philosophers make in motivating the non-identity problem. Let's review the reasoning that's supposed to generate this problem. Let's imagine Nelson is brought into existence in circumstances C1. In order for Nelson to have been harmed by being brought into existence in C1, then there must be some other circumstance C2 in which Nelson could have been brought into existence which would have been better for Nelson. But (the reasoning goes) in any circumstance beside C1, the individual brought into existence would not have the same genetic constitution, and so would not have the same identity, as Nelson. Hence, there is no other circumstance into which Nelson could have been brought into existence, and so Nelson could not have been harmed by being brought into existence at C1. (And the point generalizes: No one is ever harmed — or benefitted — by...