Are you talking about some new attack? The "51% attack" is a security property that fell out from the design of bitcoin: A cooperating group of people needs "51%" of the computing power to break bitcoin.
No, I'm saying that when people realised that there is a hypothetical attack that undermines bitcoin, if you have 51% of the power, that realisation didn't kill bitcoin.
51% attack publication didn't kill it.
Silk road bust didn't kill it.
Selfish miner attack publication didn't kill it.
I'm not saying that a flood of sellers won't lower the price dramatically. But to say a rumour is "all it will take" is to ignore recent history.