Look, this is not complicated.
Not indexing
#fediverse content without explicit opt-in means some people knowingly don't have access to a feature they want, i.e., a comprehensive index of other people's content they can search.
Indexing
#fediverse content without explicit opt-in means some people's privacy is unknowingly violated so they can't do anything about it.
Your _desire_ for the content to be indexed doesn't trump other users' _right_ to privacy.
#privacy1/2