I don’t think banks are the ones against Bitcoin. It should be the government that is against Bitcoin because they don’t have control over it. The banks actually report to the government and because Bitcoin isn’t doing the same, they don’t like it. Because starting from tax and other things they’d have implemented or rule they’d have set, they can’t. Bitcoin takes out the middle man and the government can’t do nothing about it, no matter much they dislike it.
The government own and regulate the banks. All other private banks are been controlled and regulated by the central bank of that country, they can’t do or undo anything until they get the permission from them which makes them centralized under the government. Bitcoin have been able to close that bridge and make it difficult for government to regulate and keep rules for. One thing about government fighting bitcoin is that, what you don’t create, you can’t destroy it. The customer base of these banks which in turn replenish back to the central banks from revenues generated from their staffs through tax has become difficult and not optimally sustainable for them after the introduction of bitcoin, so they will fight bitcoin will all they have but cannot still achieve what they aimed at.