when spam happens, the mod team just starts kicking them off, and if the payment is too low it can be dynamically adjusted until the spammer cannot afford it. ie, if the payment for a user was 7000 sats, then a spammer would have to pay 7000 sats per message. users that already signed up are unaffected. this is a game they cannot win, but only if we can find ways to expose it to the users because otherwise they won't sign up at all, get spammed, and then leave nostr.