I need/use write access for creating bookmarks and private statuses (for copying Nostr content into new private notes). Without that, usability would be greatly reduced, or I would keep data on my server. The functionality you desire is what I am providing. Data is kept on my server and potentially anonymously evaluated (ID is only saved hashed, which of course can be undone by rehashing all IDs and seeing which one matches). 

 All data that can be saved in your Mastodon account is saved there.