Were There Dinosaurs on Noah’s Ark? - Jeffrey Goldberg - The Atlantic

It's all about manipulation and control.  Without Genesis, the creation narrative, there is no Christ and he becomes just another myth.

Sitting with Ken Ham and Terry Mortenson, a historian of geology and a theologian on staff, I asked why it is so important to convince their visitors—more than 2 million since the museum opened seven years ago—that Genesis is a book of history. "There’s a slippery slope in regard to authority,” Ham replied. “If you say that the history in Genesis is not true, then you can just take man’s ideas as true. When you go outside of Scripture, why shouldn’t you just reinterpret what marriage means? So our emphasis is on the slippery slope regarding authority.”
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Mortenson stayed on the subject of gay marriage. “The homosexual issue flows from this. Genesis says that God created marriage between one man and one woman. He didn’t create it between two men, or two women, or two men and one woman, or three men and one woman, or two women and one man, or three women and one man. If other parts of Genesis aren’t true, then how could this idea of marriage be true? If there were no Adam and Eve and we’re all evolved from apelike ancestors and there’s homosexuality in the animal world and if Genesis is mythology, then you can justify any behavior you want.” I found this preoccupation with gay marriage significant, because it suggests that perhaps at least some of those who profess a belief in creationism might simply be signaling their preference for a more traditional social order, rather than a rejection of modern science and free intellectual inquiry.

Were There Dinosaurs on Noah’s Ark? - Jeffrey Goldberg - The Atlantic