It's an illusion to believe Bitcoin is a completely trust less system. We need a majority of miners to act responsibly. This has shown in the 2013 database fork and recently with the lazy block validating.
There is no problem trusting the miners - only with pools controlling too much mining power.
Last time I checked, the top 3 pools and the top 4 Chinese pools had ~55% of the total hashpower. The top 5 pools (the Chinese one plus the Ukranian BitFury) had over 70%.
Objectively, bitcoin failed. Users and holders must trust that those top 5 miners will not do anything nasty. If they conspired to put all other miners out of business, they could do it. If they agreed to block an account forever, they could do it. If they agreed to make some change to the protocol, they could easily force everybody do accept it. There would be much cursing ang grawing of teeth, but the only choices for all users and holders would be to either accept the change, of lose their coins. Since the whole point of bitcoin was to eliminate the need to trust an intermediary, the system has become pointless.
It is often stated that miners don't have that power, and it is the "economic majority" that matters; or that they will never want to do it because "it would destroy the value of their investment". That is bullshit, it is the fairy tale that has been spun to hide a problem that has no solution. Indeed, if the miners do force a change in the protocol, those same people will spin the tale that it was no big deal, that the change was in fact approved by the majority, that it is in fact "good for bitcoin" etc. -- because, like now, the value of their investment will depend on preserving the
public image of security and stability.
By the way, we know that the Chinese miners
can get together and agree to a common policy, with
a document signed and stamped with red stars.
This is not the way that bitcoin was supposed to be. Implicit in the original design was the assumption that, while full relaying nodes might end up restricted to businesses that could afford to run a server 24/7, mining would be done by ordinary clients, as an alternative to buying coins. As long as that was the case, having the integrity of the system depend on a mining majority would actually ensure the independence and security of the system.
Satoshi was quite upset when someone published the first GPU mining program, because such greedy miners would invalidate mining by ordinary clients. That problem unfortunately got worse and worse, ending with the current situation -- where the network is just one small step away from being run and controlled by a closed consortium of private miners.
The immediate cause of the problem was the disparity between the fixed block reward (currently 25 BTC/bk) and the market price of the coin (currently 270 USD/BTC). That combination made mining into a business with an extremely large revenue stream, now still ~1 million USD/day By comparison, BitPay, the largest bitcoin payment processor in 2014, processed less than 0.5 million USD/day during that year -- including payments related to mining (i.e., internal to the bitcoin system as a whole) and purchase of precious metals (which was basically investors switching from bitcoin to another investment asset). Even assuming that BitPay processed only a fraction of all the e-payments using bitcoin, the cost of maintaining the network (including or excluding the miner's profit) is totally out of proportion to the actual use of bitcoin as a currency -- the purpose for which it was designed and implemented.
The high price of bitcoin, in turn, resulted from speculative investment, fueled by expectations of extremely high value in some vague future, based in turn on its alleged scarcity, "deflationary" character, and dreams of it capturing a significant slice of the credit card market. While the future may still bring surprises, those claims have been largely debunked since the crash of the 2013 bubble.
Another consequence of this overvaluation of the coin is that the huge cost of mining is not borne by the users of the coin, or by its current investors, but by the new investors who are buying the coin today. Theirs is the only money flowing into the bitcoin system: that money flows out of the system as miners' revenue (1 million USD/day), the payoff of the early investors who are reducing their holdings (an unknown amount) and part of the fees of bitcoin exchanges, payment processors, and other bitcoin services (also an unknown amount, but probably much less than 1 million USD/day).
Because of this unhealthy economic structure, the bitcoin system is creating an increasing mountain of "moral debt": the money that people have invested in bitcoins, and expect to get back with at least some profit. Of course, there is no entity guaranteeing to pay this debt. It is not possible to compute this "Bitcoin National Debt" (BND), because there is no way to know the price that each bitcoin holder paid for his coins; but we can tell that it is somewhere between 400 million and 17 billion USD. The only way the current holders can recover their investment is by selling their coins to new investors; but that will only increase the BND... Obviously this snowball rolling cannot go on forever, and it can only end in tears.