Too late for 51% attack

[bitbollo]

There are more risks for the miner and probably this cannot be a real threat.
Not only because the network has become bigger and most of bitcoin has been mined...
Even if nowadays all biggest miners would collide to make their syndicate, they would never be able to collect all blocks.
Once they would collect it they could just split the effort, just create another pool.
In the meanwhile they have to compete with all others miners and placing the whole network at risk. Just to mention.. once cex.io has reached this critical level they have decided to limit the size of their pool...

[CryptoYar]

Your instinct is correct. Mining pools are not owners, but rather managers. Hashrate of a pool to which is pointing thousands of miners worldwide, every one of which being able to change target pool whenever they want. Otherwise, miners would simply walk away and attack would be canceled if pool tried any shady business.

There is also economic reward reason. Successful 51% attack would have big impact on Bitcoin price and people would lose faith in it. Those with hashrate to be able to do so are the ones most likely to lose money if BTC goes down in value. For those who own Bitcoin and mining gear, attack is self-ruining. This is because people are confusing pool hashrate with pool ownership. They are two entirely different ideas and understanding that difference makes the 51% threat from big pools imaginary, not real.

[treesintheforestooh]

Not sure I can add any more value to an old horse that died so long ago no one remembers where it's buried... but, to all who bring this up, don't think about the possiblity (everything is possible) and don't think about the likelihood (never a zero chance of anything happening) but think about "to what end?".

What could a 51% attack possibly gain for its instigators? What could be enough to cover the financial cost of that?

Then you realise a few things and understand this isn't happening, and if it does, it won't have lasting repercussions on the good actors.

A 51% attack doesn't have to come from someone/an organization/a "network state" type actor looking to make money.

Indeed, when/if the next attack comes it will very likely be political and ideological.

[legiteum]

A 51% attack would most likely come from a clandestine takeover of the systems of a few of the mining companies. This could be done by a hacker group, but more likely a major state actor like Iran, Russia or North Korea.

As for the motive, there might be some scenario where the Bitcoin network getting fouled up could make somebody a lot of money in some complicated scheme (viz. with perps selling BTC short or something), but as the poster above said, it could be just an act of terrorism or war that was the motive.

It's worth noting at this moment a fact that Bitcoiners don't like to talk about:

Bitcoin's most important defender is the US government.

In other words, the entity that has the biggest job of tracking worldwide terrorists and malign states is the US government, and the US companies that could represent >51% of the hash rate are US companies who would be under their protection.

And then there are the US billionaires who have given the US president a lot of money, many of whom are large BTC holders and would want to make sure the Bitcoin network is protected.

Then there's the US government itself, who is known to own a lot of BTC, and could very well be the owner of the Satoshi coins as well, which would give the US government a reason to help protect the Bitcoin network for pure monetary reasons.

Finally, although he's been selling off his Bitcoin, the US president, Trump, still owns almost a half of a $billion in BTC, so that highly motivating as well.

Fortunately, the US has a very good capacity here, and has enormous capacity to strike back, but one could argue that Bitcoin would be very vulnerable to attack without the USA.

[X-ray]

That is exactly what some people don't understand, those mining pools aren't owner of hashrate, it's just a pool and whoever the hashrate belong to can get out of the pool if they disagree.

I think we've had similar thing where a pool grow beyond 51% of total hashrate and a lot of people pulled out their hashrate to decentralize decade ago.