That's still a lot to trust. How do I know someone isn't just gonna go crazy? How do I know someone isn't shorting bitcoin? That's rational.
Someone could short Bitcoin Cash and then mine in secret using Bitcoin ASICs and make a fortune screwing the whole Bitcoin Cash chain with their superior power. Proof of work sucks!
It's not though because it takes a lot more than one individual to go crazy. It takes a huge number of people, who have a huge amount invested in the platform, to simultaneously go crazy and burn their hundreds of millions of dollars worth of their own assets down. People who own that much are generally mentally stable and focused individuals, and the idea that such a huge portion would spontaneously go crazy at the same time is extremely farfetched.
Relying on cryptoeconomic incentives is a much safer bet than trusting that a handful of trusted third parties won't be bent to the will of some political elite who pass a law, or won't collude to raise fees once they have attained a significant network effect and customer lock-in.
The mining has ALREADY been centralized in a small number of mining pools. They become a cartel that charges high fees, no collusion needed. You have only one miner every 10 mins, and it has to take every transaction made in the whole world. You call that a good scalable design. Not to mention they can just be DDOSed.
But anyway tell me again why it's not rational behavior for someone to mine Bitcoin Cash in secret and then unleash their far longer chain, after shorting Bitcoin Cash on the exchanges? Why is Bitcoin Cash even secure at all?
2. No one said that proof of work based cryptocurrencies can't be attacked. Obviously there's no such thing as an invincible protocl. The point is that it is much more costly/difficult to stop a proof of work based cryptocurrency than one that depends entirely on a small set of known and trusted third parties.
>>The mining has ALREADY been centralized in a small number of mining pools.
Already been addressed in my previous comment.
>>But anyway tell me again why it's not rational behavior for someone to mine Bitcoin Cash in secret and then unleash their far longer chain, after shorting Bitcoin Cash on the exchanges?
It would be much riskier than simply mining honestly. If they short it and their attack fails, they would lose a huge amount of money.
The fact that miners do not need to be known and trusted third parties means that there is great difficulty for any network adversary to identify enough miners to make an attack effective, and that even they were able to identify pools controlling >50% mining power, they would have great difficulty sustaining this attack as the network reacts by switching to new pools.
These facts in turn make it unlikely that a network adversary would
1. target miners in an attack as a means of controlling/obstructing the network
2. succeed in causing long lasting harm to the network in the event that they attempted such an attack.
Ripple's set of known and trusted validators can very easily be stopped and controlled by any reasonably powerful set of state level adversaries, and are themselves in a position to extract rent from the network due to the potential for such a group of known parties to collude, and the coordination problem that users of the network would have in hard forking away from such a colluding set of validators.