There is no possible logical reason for being moral. Logic only operates
within an agreed model. That means it is only possible to be logical about
moral questions if both parties have agreed to work within a model for
settling questions of right and wrong. In that sense there is logic within
a Marxist, or Original Buddhist, or Zen Buddhist, or Islamic model of right
and wrong. But there is no way to prove one or the other model is the correct
(logical) one. The amoral person is not one who is bad, but a person who
refuses to discuss right and wrong at all.
For a Judeo-Christian view of how moral discussion is based on the Ten
Categories of Moral Judgment (Exodus 20) see the book
Adultery : An Exploration
of Love and Marriage