Let`s us say that a exchange got hacked, Would there be anyway to ban those bitcoins? like blacklist the stolen coins so they cannot be used on the network? I know about going back in time with consensus of the network to a earlier block or forking and using that new chain, but could you just not ban the stolen coins? I mean make a way to do that?
Bitcoin's protocol doesn't know anything about stolen coins, transaction are valid when they are signed by corresponding private keys. It's impossible to mark coins as stolen automatically, so to do this we would need to change the protocol and introduce a trusted third party to do this, but wait a second, Bitcoin was created to remove all trusted third parties, which it successfully did, and now you want to introduce them back? That would turn Bitcoin into Paypal, except it would be shitty, because fees are higher and speed is slower.