We discussed this today:
nostr:note1cw6sahfn88889uq8s642pk6sgeush4jv6c70pnzvksppltrew0kqfl9w85
tl;dr: I would use zaps or invite codes to onboard unconnected newbies. Storage and bandwidth are limited, so it is not possible to allow unlimited write access to everyone. As Nostr becomes more popular, any spam opportunities will be exploited. Regexes, IP rate limits, PoW are just band-aids that can be circumvented.