> ...the block chain is controlled by Chinese miners, just two of whom control more than 50% of the hash power.
That's a pretty unique situation.
If a predominant amount of hash power were concentrated in China, but distributed among some large (100+ to 1000+) number of miners, that would be fine. But a system of any kind is no longer decentralized the moment more than 49% of that network is entirely controlled by a small [enough] group of people.
A pool is not a single entity, it's composed of hundreds, thousands of miners.
To do some evil thing they will have to convince all of their miners to participate, and stay quiet at the same time. And all for what? So they can perform a >50% attack, crash the value, and ruin their investment?
I would worry more about things like BitFury's ASIC datacenter, which is a true singular entity.
Unfortunately miners don't get to make any real decisions about e.g. which transactions to include when running on a pool - so for arguments of decentralization the pool is one miner. Of course the miners can move to a different pool if bad things start happening, but it's only reactionary.
There's some neat tech that gets around this that is compatible with Bitcoin, for example p2pool. It's not super popular yet but it solves some of these problems.
Okay, so we need to trust three people, or whoever has the biggest datacenters.
The US Financial System relies on more than just Bank of America, Chase, and JP Morgan btw. There's more decentralization in the status-quo than the three or four big-name BTC Miners.
> ...the block chain is controlled by Chinese miners, just two of whom control more than 50% of the hash power.
That's a pretty unique situation.
If a predominant amount of hash power were concentrated in China, but distributed among some large (100+ to 1000+) number of miners, that would be fine. But a system of any kind is no longer decentralized the moment more than 49% of that network is entirely controlled by a small [enough] group of people.