Do you even know what a 51% attack is? Do you know what can be done using it? Do you know what would happen if a pool tried to do it?
Let's do a mind experiment. Assume BTC guild, right now, has 60% of all the hashing power. Now explain to me exactly what they would do in order to pull off a "51% attack", exactly what they would accomplish by doing it and most importantly exactly why they would do it.
This ^^^^
My biggest fear is that the Star Trek Enterprise will come back through time to our century and pull off a 51% attack.
I think they are only ones with their super advanced technology that could pull it off.
Hell, Commander Data could probably do it with his positronic brain.