we are approaching very fast to the point of no return when bitcoin will be the only online payment Possible via the internet. (as accelerating debt will destroy paypal,credit card companies and banks)
Come on, sure banks can get in trouble if too many loans don't get reimbursed, but Paypal doesn't care about the value of the currency they carry... they just make whatever money there is move...
Don't think the banks will let the bitcoin destroy them. They will do all in their power (and they have a lot) to kill the bitcoin if it become dangerous for them. They have the government working for them to make laws in their advantage.
Similarly, why would banks be threatened by Bitcoin? If they think there is money to be made, I don't think they'll fight it, I rather think they'll invest into it!