"If you can turn intercourse into something other than the reproductive type of act (I don't mean of course that every act is reproductive any more than every acorn leads to an oak-tree but it's the reproductive type of act) then why, if you can change it, should it be restricted to the married? "Restricted, that is, to partners bound in a formal, legal, union whose fundamental purpose is the bringing up of children?
"For if that is not its fundamental purpose there is no reason why for example "marriage" should have to be between people of opposite sexes...
"If contraceptive intercourse is all right, it becomes perfectly impossible to see anything wrong with homosexual intercourse."
-- "Contracepton" (1972) Elizabeth Anscombe
She was of course against all this, but saw that the non-Christian could folow her logic, while (unlike her) approving of he result: the polymorphous pervert would agree that if contraception is OK, anything you can imagine is OK.
But even in 1972, ever in Britain, it was still possible to hope that many readers would agree that contraception is wrong because the logic of contraception is that "Sex is anything you want it to be."
Her whole essay (it's 16 pages) is here:http://www.orthodoxytoday.org/articles/AnscombeChastity.php
Permitting contraception to the MARRIED at least still preserved a vestige of “principle.” The same principle by which in the older, wiser days we still would smile upon marriages of the senescent set, obviously well past child bearing years. Nobody told 70 year old Aunt Bertha that she shouldn’t marry because children would be impossible.
Sex outside marriage blows the principle galley-west.