Personally, legacy is but another grasping of the ego. It is meaningless and is most used as a justification to be selfish. I think kids are beyond that, it isn't something that is rationalized, it is just a means of life. And that is cool. I'm not pro or anti natalism, it all just seems to be a case of some people clinging to concepts and ideas just a little too strongly. But ultimately it has the same amount of meaning as a single ant that died a million years ago.
Also what if you cannot create genetic legacy?
Within my world view, if you cannot create a genetic legacy, you have failed at a key aspect of life.
And actually, a non-genetic child might be nice, especially if you get one at the right age. You don’t have the intense burden of raising a baby or when they’re a young child, but still get to the joy of raising a child (as long as they like you, which is of course the biggest downside. Probably less of a tendency for them to attach strongly to you).