You need to read something by Gauthier or Binmore. The idea that morality is closely related to rational self-interest is hardly a crackpot idea. There are at least two lines of argument pointing in this direction.

One derives from Hume's point that a system of morality must not only inform us as to what actions are moral, but also show why we should perform only the moral actions.

The other observes that "moral facts" are simply our moral intuitions, and that those have been shaped by evolution into a pretty good caricature of rational self-interest.

A 'morality" which takes into account the power of others may be un-Christian, but it is hardly inhuman.