How is monetary policy sustainable, or even fair, in the current economy?
IMO I think this is a good question. It's thought out and asks some interesting questions.
However, it covers several topics which makes it difficult to answer in a single answer.
I suggest we break it down, perhaps into five questions.
Additionally, the phrasing of some of the questions aren't really economics.
For example:
How is this fair for every other constituent in the economy who has earned money the hard way, by working and not by generating it so freely like interest returns on this free money do for commercial banks? How is inflation fair, as populations increase and every time someone gets a bank loan, new money is added to the economy over time, de-valuating everyone else's existing money?
Economics isn't really about assessing 'fairness', that would be perhaps philosophy.se.
However, this question could ask 'Do banks create money out of thin air?', or 'What value are banks contributing to the economy?'.