Thou shalt not lie with mankind, as with womankind: it is abomination.
The Church abolished some precepts of the Old Testaments, so each time you make a reference to the Old Testament alone, someone would challenge it on the grounds like "but we don't stone for adultery anymore, do we?"
The condemnation of the same sex "marriage", and even same sex sexual practices has to come from the specifically Christian view on human sexuality. It can't come from the Old Testament alone.
This is NOT an actual interview with Pope Benedict, let alone with the present Pope, Francis. It is an assemblage of some of Pope Benedict's statements on the subject of homosexuality. The content is the selection of Mr. Akin, not everything Pope Benedict has said or written on the topic.
It is very likely that, at some point during his long career as a theological writer, Pope Benedict mentioned the Old Testament prohibitions on homosexual behavior, as well as the many relevant New Testament passages.
What purpose would quoting the Bible to people who don’t accept it serve?
Even those who revere Leviticus as Scripture are often hard-put to explain why they consider 9/10 of it irrelevant to their own personal behavior, let alone public policy. Unless you offer animal sacrifices, segregate menstruating women, and keep kosher, I'm talking about you, too.
That's why it's actually indispensable to explain moral abhorrence of perverse sex acts, in terms of Natural Law.
It's not slighting God. He is the Author of both the Book of Scripture and the Book of Nature.