Oma honest note, if you come to think of if hackers or the bad guys per say out there aren't really looking for the fall of bitcoin rather what they are looking for is ways to steal and accumulate Bitcoins as much as they can. I bet you 9 out of 10 hackers will pick stealing bitcoins over crumbling the network , it's basically the same reason even when the 51% rule exists, literally almost no one is aiming to use it against the network rather they want to use that hashrate as an opportunity to make far more profit instead.