> Proof-of-work is what allows you to successfully combat bots, spam, and trolls, as it brings real cost to destructive actions 

Spammers are willing to spend money to spam.
They go as far as buying lists of email addresses, they'd have no issue running POW algorithms if they need to.

If anything spammers may be more willing to pay than the average social media user.
Paywalls don't protect you from spammers. See spammers on Twitter with the "verified" badge. 

 The proof of work was invented in 1993 by Moni Naor and Cynthia Dwork as a solution for email spam. I think one of Satoshi’s main contributions was the adjustable difficulty. I guess that to make the PoW concept work in social media, we need to somehow adapt the adjustable difficulty. 💭🤔 

 Scammers are trying to make money.
Sometimes you need to spend money to make money. Why would scammers not be willing to spend some money?