If someone - in this case, a mining-pool called GHash.io - can potentially mine 51% of Bitcoin, then they would effectively 'control' Bitcoin.
No, no, no, that won't happen, we won't do that, they said.
Ah, too late! They already have!
Who are we? Who cares - we have great graphics!
Time for a Hard Bitcoin / Blockchain fork, perhaps, to stop "selfish mining."