A Fine Gael TD has argued that most unwanted pregnancies are a result of fornication.
Michelle Mulherin, from Mayo, rejected calls for the Government to pass a Bill allowing abortion in cases where a woman's life is in danger.
"I'm against abortion in any form. The grace of God is so liberating and provides so many options to get the best out of life," said Ms Mulherin.
The TD, from Taoiseach Enda Kenny's constituency, added that there would be no unwanted pregnancies or unwanted babies in an ideal world, and said she worried about "the weak".
She said: "The fairer and more autonomous people become, the more responsibility they assume for their lives. They exercise that freedom by rejecting the authority that seeks to nanny them."
Ms Mulherin said no one should have unsafe sex in today's society, given the dangers of Aids and other sexually transmitted diseases.
"Fornication is probably the single most likely cause of unwanted pregnancies in this country," she said.
However, the TD then went on to insist that the Government should not legislate on religion, likening abortion to other sins such as greed, for which there are no laws.
The abortion debate was sparked by a Private Members' Bill by TDs Clare Daly, Joan Collins and Mick Wallace. It was later rejected, with 109 votes to 20. The Technical Group of TDs were calling for the Government to legislate on the controversial X Case: a 20-year-old Supreme Court ruling that women should be allowed an abortion in Ireland in the event the mother's life is in danger.
Labour TDs were among those who rejected the Bill, even though the party's national conference last weekend unanimously passed a pro-choice motion.