People on average increase in societal value from conception to childhood, and then it gets more complicated from there depending on how they turn out. And yes, typically their value declines as they become elderly.

But, as in your example with your adopted friend, even a baby that starts out unwanted, if society invests a bit in its welfare, will soon become part of the social fabric and so on and thereby become valued.

Certainly there are some people who literally nobody likes, but even then, there's still reason B.

As it happens, my best friend was adopted as well. But I hardly think the limiting factor in the number or quality of my friends is society's production of babies.