There is no any monopoly over currency exchange. You can go in a bank and exchange your money by bank's prices or can go in a street exchanger and exchange there. The world is too far from the bank's monopoly, baddy 
Street exchangers work for banks or are owned by banks.
You don't exchange anything without banks being involved.
Cashless society is a banker monopoly, and a bad idea.
You make a few false assumptions in your post
First, banks and large international corporations are essentially the same. Some corporations even set up their own banks (though the connection may be not open, of course), so they can't possibly steal their own money. Further, you erroneously assume that the wealth of both big and small corporations consists in money they keep in banks. This is obviously not so. Even the largest corporations may have a very small amount of money in their bank accounts, just enough for current operational expenses. And if these expenses are small it doesn't make sense to keep plenty of money in the bank account
Almost anyone living in a capitalist country can start a corporation
To start a bank you need sufficient capital
If you have that, you can start a bank, as plain and simple as it gets. This is certainly not about "no one is allowed to start a bank". Apart from that, I don't see what it has to do with your point. Further, it is not my idea that big corporations can and do establish their own "pet" banks (I have provided you a link). In fact, many international or just large enough companies which started as pure production (or whatever) firms are now part of large financial groups which include banks to serve the interests of these groups. The fact that Facebook doesn't have a bank means that it is not a corporation (which it is not) or it doesn't need a bank, just as simple. I don't understand why you continue this futile argument