Then Judah said to Onan, "Lie with your brother's wife and fulfill your duty to her as a brother-in-law to produce offspring for your brother." But Onan knew that the offspring would not be his; so whenever he lay with his brother's wife, he spilled his semen on the ground to keep from producing offspring for his brother. What he did was wicked in the LORD's sight; so he put him to death also. (NIV, Genesis 38:8-10)
What Onan did was not masturbation, but a form of birth control known as coitus interruptus. Onan's actual sin was probably his resistance to the Old Testament custom of providing offspring for his deceased brother by impregnating his widow. However a parallel is sometimes drawn between Onan's act and the wasting of the semen that occurs when males masturbate.
Data from the sciences have also severely challenged the traditional condemnation of masturbation, which to some extent was based on outmoded views of human reproduction. At one time it was believed the male sperm was the only factor in human reproduction and the sperm was regarded as humans in miniature. Hence spilling it out was tantamount to abortion as well as a waste of a precious element. Other myths also played a role. Masturbation was blamed for a whole host of physical and spiritual ills such as acne, asthma, heart murmurs, lethargy and even insanity.1
It is now known that sperm cells are not miniature humans; a man's sperm must unite with a woman's egg before a baby can be formed. Furthermore, sperm cells not ejected from the body simply die after a few weeks anyway, and they are continuously replaced. It is also now known that masturbation does not cause acne, insanity or any of the other ills it was blamed for in the past.
Psychological data indicate that masturbation is common in both sexes and all age groups, particularly adolescents. It may create a sense of guilt that is blown out of proportion by the taboo nature of the subject.
Among the three largest Christian denominations in the United States, the official Catholic Church teaching is below. The Southern Baptist Convention and United Methodist Church do not have official statements about masturbation.
2352 By masturbation is to be understood the deliberate stimulation of the genital organs in order to derive sexual pleasure. "Both the Magisterium of the Church, in the course of a constant tradition, and the moral sense of the faithful have been in no doubt and have firmly maintained that masturbation is an intrinsically and gravely disordered action." "The deliberate use of the sexual faculty, for whatever reason, outside of marriage is essentially contrary to its purpose." For here sexual pleasure is sought outside of "the sexual relationship which is demanded by the moral order and in which the total meaning of mutual self-giving and human procreation in the context of true love is achieved."
To form an equitable judgment about the subjects' moral responsibility and to guide pastoral action, one must take into account the affective immaturity, force of acquired habit, conditions of anxiety or other psychological or social factors that lessen, if not even reduce to a minimum, moral culpability.3
1Thomas Bokenkotter, Essential Catholicism, Doubleday, 1985,
2Anthony J. Wilhelm, Christ Among Us. A Modern Presentation of the Catholic Faith for Adults, Fifth revised edition, HarperSanFrancisco, 1990, p.351
3Catechism of the Catholic Church, Second Edition, www.usccb.org/beliefs-and-teachings/what-we-believe/catechism/catechism-of-the-catholic-church/epub/index.cfm