the million dollar question is what the government and big organizations think of Bitcoin ? in which position Bitcoin stands ? is bitcoin a threat for them ? will they ever regulate bitcoin ?
it is a serious matter that should be discussed but when you have the answers to these questions it will be easier to imagine the 51% attack.
First, you have to ask who is "the government". Big corporations, capitalists and other criminals including several lawmakers and politicians from all countires in the world sent billions to tax havens for decades. Now the FED and the governments are raining their parade by printing zillions and blocking capital movements. Bitcoin could be seen as a new "haven". And these guys were able to convince DC that wiring money to a dubious corporation in "Cayman Islands" is lawful, I don't doubt that they can lobby DC and Berlin in favor of bitcoin, even if bitcoin is bad for the government is good for the elites that run the show.