There's a good chance the authorities are behind the DDOS attacks. Or ripple/litecoin supporters
But yeah I would chip in a few bitcoins to protect bitcoin.
It's probably the bankers behind it, they'd have the money and resources to do it and who has more history at manipulating markets in their favour than them.
I wouldn't be surprised if they hire groups of hackers to perform these attacks when they want.
I could be wrong though!