[brandonsometig]

To be in the position of being able to do a bitcoin 51% attack however you would have had to sunk enormous costs into buying ASIC miners. The minute everyone finds out that a 51% attack occurs you will have pressure to change the mining algorithm and suddenly all your miners are worthless.

[bb88]

What jhpriestley pointed out is that what's really saving bitcoin from a 51% attack is the inefficiency of obtaining computing power.

If renting asic miners becomes vogue (and it might because it makes the computing market more efficient) then it might be possible just to rent asic miners for nearly free, since you'd be acquiring bitcoins while you were amassing the 51% computing power.