That depends. Currencies are used for paying each other and accounting for usage. Sites like HN and Reddit have a "currency" like Karma. If Wikipedia operated its own currency, it could reward helpful contributions and make vandalism costly (you'd lose 10-50% of your currency if you were found to have vandalized a page, etc.) You can see a quick overview here:
https://intercoin.org/communities.pdfAlso, micropayments are essential for a truly decentralized market. I suggest you read this: https://qbix.com/ecosystem
Xanadu used to have the idea of micropayments. You can do those with trustlines which settle eventually on a decentralized ledger.
We're not the only ones working on this. Stefan Thomas (I met him when he was CTO of Ripple) left Ripple to work on his true love, Interledger Protocol, and started Coil. A few years back, Mozilla joined forces with Coil to offer a $100 Million dollar fund for Web Payments (that don't need the banking system): https://foundation.mozilla.org/en/blog/100-million-investmen...
The creator of Javascript, Brendan Eich, left and started Brave Browser, which had a currency for monetizing people's attention, instead of the Surveillance Capitalism economy that's pervasive in all the centralized walled gardens: https://en.wikipedia.org/wiki/Surveillance_capitalism
BitTorrent (the largest decentralized network by traffic) launched the BTT token, to help incentivize traffic.
The IPFS folks (who are helping decentralize the Web and ) did a $200M ICO for their coin, which helps pay for storage.
The guy who started AngelList, Naval Ravikant, launched CoinList and helped them do it, in a legal way, and involved many Web2 VCs participating in that ICO.
You're going to have to hate a lot of Web2 greats in order to carry out the hate of Web3 to its logical conclusion. Perhaps HN is wrong to simply hate the idea of decentralized currencies?