Money simply facilitates transactions, capital requires a return.

I would say firstly that unsecured credit facilitates transactions, and has a cost consisting of shared system costs and defaults.

Secured credit and conventional Equity in a Corporation are the conflicting financial claims (financial capital) over productive assets (industrial capital) which require a return.

However, this return is paid for from the sale of production/ use value of the relevant productive assets.

Ther is nothing wrong with a cost of credit or a return on capital per se.

The key problem lies in the fact that interest-bearing credit currently is money.  The increasing inequalities in access to this credit combine with exclusive ownership of productive assets - and particularly the Commons of land, non-renewable resources and knowledge - to create a continuing and finally unsustainable transfer of wealth.  

"The future is already here -- it's just not very evenly distributed" William Gibson