Someone with some real cash(like a bank) can easily kill bitcoin just by achiving 50% of hashrate or destabilize it by joining the biggest pool swealing it to 51%. Currently it wouldn't be so hard to do, it's just under the radar of big realworld intitutions.
It's not so easy. Right now Bitcoin is by far the most powerful computing network on Earth, so it would be extremely expensive to even briefly execute a 51% attack on their own.
Joining the biggest pool (deepbit) gives the decision-making power to the pool owner. So joining actually reduces their ability to attack - if the banks coerce the pool owner into attacking, everyone else joins another pool.
And we're not under their radar:http://mobile.reuters.com/article/idUSBRE83108120120402?irpc=932
If anything, they'll try to embrace, extend, extinguish. An overt attack would be foolish.