Good Abominations?

Mary Douglas, in Leviticus as Literature, points out that Leviticus 11 should really stun the careful Bible reader. If we recall that God is the Creator of all things, and that He not only created all things but also declared all things good, how can some of them be "abominations" to the Hebrews? How are so many animals "unclean"? Why can't God's people touch or eat so many of His good creatures?

Even after the Fall, Noah saved unclean animals in his ark from the flood. If they were abominations, why would God want Noah to save them? Why not destroy them in the flood? Why not have Israel destroy them in the land of Canaan along with the Canaanites who do abominations?

How is separating from these creatures an act of "holiness" (Lev. 11:44)?