If an instance allows anyone to sign up then I think they need to tolerate those users having different tastes and interests, within reason. Most instances have policies against illegal content, and many don’t allow porn. Defederation is the tool instance admins can use to prevent subscriptions to content they don’t want to host. Other than that, if other users don’t want to see certain content, they can simply not subscribe to it and avoid the All feed. Personally I like browsing All precisely because it shows me things I didn’t know about, and might be interested in.

Currently there’s no way for users or instance admins to block specific communities. I hope that will be made available at some point, so content blocking can be done at a more granular level and defederation can be reserved for more extreme cases. Instance admins would be free to curate their All feed if that’s what they want to do. Users would be free to pick an instance that suits them, possibly one with a heavily curated feed or instead choose one that hosts a broad array of content. A broad array of content is much less likely to be an issue if users can block at the community level so they don’t have to see it.