And in practice this majority is held by a dozen or so mining pools. This is the usual schizophreny in US politics making yet another appearance: because people do not trust public oversight in the elected government they hand over the oversight to unelected private entities. No central bank, it's mining pools instead.
One would think that the leading figures of these pools know each other. One would think it's outside the realm of conspiracy to think that the designers of Bitcoin expected the mining pools to emerge once difficulty had grown sufficiently large.
> One would think that the leading figures of these pools know each other. One would think it's outside the realm of conspiracy...
No it is not outside the realm of possibility that people could conspire to perform a double spending attack, you are completely right. What you have to consider, however, it is not very likely that people conspire to undermine their own economic interest. That doesn't happen very often in this world, it is not in our nature (but it is a possibility).
There are much cheaper and easier attacks that could be pulled off right now by a single attacker, lower hanging fruit (like flooding the network with transactions with above average fees, this will effectively block most other transactions for as long as the attacker can afford).
If a double spending attack was to occur at the mining pool level, you wouldn't even need to have a conspiracy to make it possible, just a single large pool operator with a period of extraordinary luck would be able to get 6 blocks in a row (it has happened before, it will happen again).
Mining pools cannot arbitrarily modify bitcoin's policies (that is, they cannot execute a 50% attack) because each pool is comprised of tens of thousands of individual miners running third-party, open-source mining software. Miners connect to the pool just by passing a username and password on the CLI/config file. You can be connected to multiple pools at once, executing the same binary to produce results for each pool.
Bitcoiners are savvy enough to get raised eyebrows if a major pool started encouraging and/or requiring users to use a proprietary, closed mining software that may attempt to modify the bitcoin network's behavior to do something unsavory.
One would think that the leading figures of these pools know each other. One would think it's outside the realm of conspiracy to think that the designers of Bitcoin expected the mining pools to emerge once difficulty had grown sufficiently large.