I don't see anything more or less ethical here. The bank has to get a return. Whether it does so through interest or a "share of the profit" is more a matter of

I don't see anything more or less ethical here. The bank has to get a return. Whether it does so through interest or a "share of the profit" is more a matter of risk and transaction cost. It's hard for me to believe that what it costs to maintain a knowledge of a borrower's profit and then collect from that is really competitive.