> Basically, it seems like the terminal state of this is a gigantic freeloader problem where everyone wants the network to be secure but nobody is incentivized

> Basically, it seems like the terminal state of this is a gigantic freeloader problem where everyone wants the network to be secure but nobody is incentivized to do it. It'll be in the interest of exchanges and payment processors to prevent double-spend at least, and they have an incentive for the blockchain to be trustworthy vs. running their own attacks and could adjust their own fees to maintain >51% control of miners across the lot of them. There's also a fallback recovery mechanism; for any attacker willing to invest $X in a 51% attack the remaining users only have to invest an additional $X*.04 to regain 51% control and make a hard fork that most miners would switch to. My guess is that faced with evidence of a double-spend most miners would switch to the hard fork to avoid losing the block rewards the attacker's chain stole from them. This relies on rapid detection of the attack and availability of a hard-fork client.