...but they didn't halt trading until they were asked to, so clearly it wasn't totally in their interests?
Exchanges are in a difficult position once the 'head' of ethereum tells them to stop. It's a sign that the blockchain might be forked, so any further trades they make might be undone - they simply have little choice but to stop after being told to do so.
> but they didn't halt trading until they were asked to, so clearly it wasn't totally in their interests?
Not at all. This is a classic "coordination problem". It is advantageous for many participants in the overall system to take an action, but only if the other participants are ALSO taking the action. In such a case, a widely followed and popular leader is one possible coordinating mechanism. And it does not give that popular leader the ability to do ANYTHING, only things that actually ARE popular but require coordination.
I don't agree. Centralised control would mean one person can change anything. Decentralised doesn't mean that nobody can propose a solution - only that others have to agree on it before it goes live.
How do you imagine decentralised decisions happening otherwise? Everyone choosing their own solution without ever talking to each other and seeing what is most popular?
I'm not sure whether we are redefining it... I suppose it depends on what definition you were starting with!
My idea of "decentralized" includes things like "continues to function perfectly well if any one person or small group is removed from the process" and "continues to function perfectly well if any one person or small group becomes malicious".
In this case, if Vitalik Buterin were not around to announce the problem, someone else could announce it and that would provide a coordinating signal for all of the independent players to act on. If Vitalik Buterin were malicious and decided to announce a rollback of a big spend he had done, then the independent miners and mining pool operators would (I hope) choose to ignore the announcement and refuse to participate.
I guess to me, having a centralized group or individual make decisions seems to violate "decentralized", but having one of several possible groups or individuals make announcements which signal the population to take action does not.
Nobody has to follow the leader. Want to keep your exchange trading? Go ahead - nobody can stop you. It just so happens that everybody agrees this time.
A surprising number of people seem to believe in the near-perfect efficiency of markets, that every participant is making optimal decisions based on their own goals.
Exchanges are in a difficult position once the 'head' of ethereum tells them to stop. It's a sign that the blockchain might be forked, so any further trades they make might be undone - they simply have little choice but to stop after being told to do so.