It's possible to trick grandpa into sending money to Nigeria, too, but we don't use that as an excuse for forcing him to do business with a particular bank.
Nobody sane would argue that our current approach to banking security is fine, though. There definitely is money to be made with more secure and convenient money transfer, as proved by the quite large number of start-ups in the field. Among these, quite a lot work only among users of the same app without anybody being outraged about it.
