This is a post written by David Thorstad, a philosophy professor who maintains a blog for criticizing various tenets of effective altruism called Reflective Altruism, as part of a series of on human biodiversity (HBD), a modern iteration of so-called race science. HBD, of course, isn't typical fare for EA, or any of its championed causes. Yet it has, to much controversy over the years, been recognized as a subject of interest among prominent thinkers associated with either the effective altruism or rationality communities, or others writers they've been affiliated with. This latest post in Thorstad's series provides a critical overview of @Scott Alexander's history of engagement with said body of ideas, both on his current blog, Astral Codex Ten (ACX), as well as before then, such as on his previous blog, Slate Star Codex (SSC).
I'd say an obvious difference is that EA family planning orgs aren't doing permanent sterilization.
I'd also say that the reason Thorstad is upset is probably mostly because he sees Scott's support for the org as "let's get rid of drug addicts children from the next generation because they have bad genes", and-rightly in my view-worries that this is the sort of logic that the Nazis used to justify genocide of the "wrong sort" of people, and that if HBD becomes widely believed people might turn this logic against Black people. Scott could (and would) reasonably protest that there is a big difference between being prepared to use violence for eugenic goals, and merely incentivizing people towards them in non-coerceive ways. But if you apply this to race rather than drug addicts "we should try and make there be less Black people, non-coercively" is still Nazi and awful.
This sort of eugenic reasoning doesn't actually seem to be what's going on with Project Prevention itself, incidentally. From the Guardian article, it seems like the founder genuinely values the children of drug addicts as human beings, given she adopted them, and is just trying to stop them being hurt. From that point of view, I'd say she is probably a bit confused though: it's not clear most children of addicts have lives that are worse than nothing, even though they will be worse than average. So it's not clear it actually helps them to prevent them being born.