Large blocks make it too costly to run a full node

Greg Maxwell writes: "Today Bitcoin Core is easily >100 times faster to synchronize and relay than when I first got involved on the same hardware, but these improvements have been swallowed by the growth. The ironic thing is that our frantic efforts to keep ahead and not lose decentralization have both not been enough (by the best measures, full node usage is the lowest its been since 2011 even though the user base is huge now) and yet also so much that people could seriously talk about increasing the block size to something gigantic like 20MB."

Peter Todd writes: "Even a relatively small increase to 20MB will greatly reduce the number of people who can participate fully in Bitcoin, creating an environment where the next increase requires the consent of an even smaller portion of the Bitcoin ecosystem. Where does that stop? What's the proposed mechanism that'll create an incentive and social consensus to not just 'kick the can down the road'(3) and further centralize but actually scale up Bitcoin the hard way?"

Pieter Wuille writes: "*using* a full node for validating your business (or personal!) transactions empowers you to using a financial system that requires less trust in *anyone* (not even in a decentralized group of peers) than anything else. Moreover, using a full node is what given you power of the systems' rules, as anyone who wants to change it now needs to convince you to upgrade. And yes, 20 MB blocks will change people's ability to use full nodes, even if the costs are small."

There seem to be three main costs to full node operators with larger blocks:
 * 1) Bandwidth: larger blocks means more data received from and sent to peers.
 * 2) Hard drive space: you need to store the block chain somewhere.
 * 3) Memory: larger blocks will lead to a larger UTXO set. This is currently stored in memory although the entire thing doesn't need to be for non-miners.

Raising the block size impacts all of these things.

Counterarguments

 * It is unclear which costs are supposed to be most unbearable, and the extent of the cost increase of moving to any specific block size. There is not a lot of data or analysis behind the claim that the increase would be significant for people.
 * Gavin claims the costs required for 20 MB blocks are low, and disk space shouldn't be an issue with block chain pruning.
 * These costs are reasonable for a non-poor person in a developed country, but they might price out many people in less developed countries. How important is it for a poor person in India to be able to run a full node? Their not being able to doesn't hurt the trustlessness of the network, but it does deprive them of a fully trustless experience.
 * It's likely that full node count is declining not because of the costs of running a full node, but because of the rise of web and SPV wallets. People who never cared much about running a full node for the decentralization benefits are the ones who are switching to newer more convenient wallets. People who value decentralization are still able to run a full node pretty easily, and that's what matters.