Big banks are so nervous about bitcoin because of competition on investment. Well banks are wise and has a lot of resources especialy if it is about it's competitors. Before banks even don't know about bitcoin but because of its popularity and some of the investors go thru the crypto currencies like bitcoin that was the time they knew about it. Crypto currencies can replace banks in my opinion but I guess that it will take a very long to happen. And that chance I guess is also one of the many reasons why banks are nervous about bitcoin.