A corollary to such a definition of sin is that all else is properly to be left free. Sex and selfishness, neither sinful in itself, are not learned. They are innate. Although sex urges may be dormant in childhood, somewhere in the teen years they come on with unsettling force. Philosophers talk about instincts , which is a word used to designate unlearned and unexplainable phenomena which are simple facts of creation, to be accepted despite their not being analyzable.
Selfishness is as much necessary to keep civilization going as is sex.
If there is to be no sex, there will not be more babies, and in a short time there will be no more human beings on the earth. Selfishness as indicated is identical with the instinct of self-survival. Men consider almost anything justifiable in order to survive. If a man breaks into your house and threatens death or injury, your instinct will be to disable him in order to survive yourself, or kill him condignly. The alternative to Individualism is Altruism.