@louisoft01 it doesn't have to be a privacy risk. It's opt-in, and more of a shorthand for peeling through a tree of objects containing basic public profile metadata.
Friendica and Hubzilla have had it for years, and although their combined userbases are much smaller, they have never had a problem.
There is a sane way to design this feature in a manner that doesn't suck. The biggest issue in my opinion, other than sort order, would be a reliable way to accept retractions from users who don't want to be seen in the directory anymore, after being there for a while. These are largely solved problems.
I think it would also be a good idea to hide users from the servers that they are blocking. Basically it would tell each directory on an instance "never deliver my record to domain1, domain 2, or domain 3."