The natural interest rate plus a bit.

If you can earn 25% percent in profits in the current environment then it is a clear indication of an inefficient market - a market that needs to be regulated in order to create efficiency (like in this case as with many other cases: remove monopolistic behavior).

While it is problematic if you can't derive profits from productive activities it is also problematic when entities derive unsustainable profits - also for the party deriving the profits.

If there is not a bit middle class to consume products, then there will not be be a market to supply products to.