Even if someone was having 51% of the hashing power, that wouldn't mean that bitcoin was not functioning - only, we would now have a "CEO of bitcoin".  That said, the relationship is somewhat more complicated, because that 51% power is mostly outsourced to hardware owners.  There hardware owners cannot decide directly, (they only sell their hash rate), but they are part of the "block chain producing industry" and wouldn't want to see the system destroyed in which they are hardware-invested.   So even if a single pool had more than 51% of the hash rate, I don't think it would mean that bitcoin was compromised.  The day that that pool owner "goes beserk", the hardware owners might decide to jump to another pool if the jumping of the pool owner is not seen in their lucrative advantage.

There's no reason for a big pool owner to go beserk ; however, all miners (hardware owners and pool owners) will want to find the most lucrative way of running bitcoin for them, that's for sure.   My idea is that the current protocol is actually very lucrative to them.