Agree about privacy. 

By the way, Amethyst (or any other client, I guess) can provide to any npub a shadow ban. Easily. Relays will eat your events, but clients won't show it to anyone. 

For example that's how Amethyst spam filter is working - blocking npubs without your participation, automatically. Default settings. Read the thread:
 
nostr:nevent1qqsv5ag7wy9r53g7763mjq4l66708mjle2vp3ce3v2nygv3ajtf4dmgpzpmhxue69uhkummnw3ezumt0d5hsygqcj6nhm7pe3vyvp9hy6pywf55xvdqtqawr56n9jr8ss2hfcplq8cpsgqqqqqqs0kam6v

The same about relays' spam filters. I think it may mark any account as a spam at some point and stop delivering content to other users. Maybe not all of them at the same time, but it is possible.