If you DONT want your notes to be PUBLICLY viewable and filterable by ANYBODY you have ONLY two options.
Either ENCRYPT all your notes (nip44) and post to private groups on paid relays OR don’t use Nostr.
Data on Nostr is by DEFAULT open for ANYONE to do anything they like. This is Nostr’s SUPERPOWER, and what makes (public data on) Nostr so censorship resistant.
NO a bot that scrapes ALL content is NOT akin to “big brother” surveillance, simply because it has no special access or (power to restrict access) to PUBLIC data.
I think you need to shift your paradigm. Problem solving in a decentralized space is actually more challenging …