The root problem with conventional currency is all the trust that's required to make it work. The central bank must be trusted not to debase the currency, but the history of fiat currencies is full of breaches of that trust. Banks must be trusted to hold our money and transfer it electronically, but they lend it out in waves of credit bubbles with barely a fraction in reserve. We have to trust them with our privacy, trust them not to let identity thieves drain our accounts. Their massive overhead costs make micropayments impossible.
The usual solution is for a trusted company with a central database to check for double-spending, but that just gets back to the trust model. In its central position, the company can override the users, and the fees needed to support the company make micropayments impractical.
Satoshi Nakamoto, 2009
http://wayback.archive.org/web/20110926195018/http://p2pfoundation.ning.com/forum/topics/bitcoin-open-source?xg_source=activityWhat satoshi seems to not have realized is the fact that in order to cater for mainstream-level of micropayments possible onchain, we would go back to the trust model, since the nodes would be centralized datacenters, which would be the same as having the central database. We would change centralized servers to centralized nodes. The whole thing is nonsense, we need to find a middle ground.
Satoshi Nakamoto added payment channel support since day 1 and Hal Finney mentioned the idea of the settlement layers. It's clear that we have to choose: fast mainstream micropayments offchain with decentralized node network, OR fast onchain micropayments with centralized node network