Originally posted by Pope Nicholas:
"Judah said to Onan, Go in to your brothers wife, and perform the
duty of a brother-in-law to her, and raise up offspring for your
brother. But Onan knew that the offspring would not be his; so
when he went in to his brothers wife he spilled the semen on the
ground, lest he should give offspring to his brother. And what he
did was displeasing in the sight of the Lord, and he slew him also"
(Gen. 38:810).
The biblical penalty for not giving your brothers widow children
was public humiliation, not death (Deut. 25:710). But Onan
received death as punishment for his crime. This means his crime
was more than simply not fulfilling the duty of a brother-in-law.
He lost his life because he violated natural law, as Jewish and
Christian commentators have always understood. For this reason,
certain forms of contraception have historically been known as
"Onanism," after the man who practiced it, just as homosexuality
has historically been known as "Sodomy," after the men of Sodom,
who practiced that vice (cf. Gen. 19). ( Cathollic Answers)
So the argument God killed him for using Contraception
stands.
Contraception is wrong because its a deliberate violation of the
design God built into the human race, often referred to as "natural
law." The natural law purpose of sex is procreation. The pleasure
that sexual intercourse provides is an additional blessing from
God, intended to offer the possibility of new life while
strengthening the bond of intimacy, respect, and love between
husband and wife. The loving environment this bond creates is the
perfect setting for nurturing children.
But sexual pleasure within marriage becomes unnatural, and even
harmful to the spouses, when it is used in a way that deliberately
excludes the basic purpose of sex, which is procreation. Gods gift
of the sex act, along with its pleasure and intimacy, must not be
abused by deliberately frustrating its natural
endprocreation.
God killed Onan for wanting to have free sex indefinitly with
his brother's wife. Essentially commiting adultery over and over
again. God looks at the heart and the intention, not the act of
contraception. This is a very clear cut substance over form
issue.