Too Long; Didn't Read
One of the most powerful properties of a blockchain is the fact that every single part of the blockchain's execution can be independently validated. How much validation do we actually need? Do we need a culture where the average person in the world runs software that checks every transaction? It's these questions, that are a challenge, and a very important challenge to resolve especially if we want to build blockchains with consensus mechanisms better than the single-chain "Nakamoto" proof of work that the blockchain space originally started with. If enough users are validating, then a contentious attempt to force a change of the protocol will default to chaos.