One thing I was wrong about over the last few years: sign up costs would dramatically reduce spam. 

Turns out spam is a top 3 problem (aside from retention and infrastructure scaling) to solve for when building a permissionless decentralized social networking protocol.

Spammers are willing to pay for sign ups at prices that normal users aren't.

Spam is also relative: what's spammy for one person is not for another.

Corollary: when you talk to developers building on Farcaster, spam is a top of mind issue whereas users giving product feedback but not actively building in the ecosystem tend to think this isn't that big an issue / not that hard a problem to solve. 

Also a good proxy for the quality of first principles thinking when suggesting "why don't you just do this?" if you haven't considered how would spammers abuse this and what's the solution.

I think crypto spammers =\= non crypto spammers. Crypto spammers (and scammers) are more willing to pay than in other industries