[runeks]

Non-proof-of-work consensus always ends up depending either on trusted third parties or majority vote. Anyone can create a valid-looking non-PoW chain in a short time, and there's no way to separate valid chains from each other. In Bitcoin, when you want to bootstrap, you connect to n nodes and if just a single node is honest you will get the right chain. For non-PoW, if there's disagreement, you have to trust either a majority on what the right chain is, or add trusted nodes that overrule a majority vote. For proof-of-work there will always be a chain with most work done, provided >50% of miners are honest (hard dependency).

I have written a bit longer on the subject here: https://runeksvendsen.github.io/blog/posts/2017-06-14-bitcoi...