Ken Ham is representative, I believe, of those who insist on a literal Biblical interpretation in the face of overwhelming evidence of an old universe. I truly believe he, and others like him, are sincere in proclaiming that;
Ultimately, the controversy about the age of the earth is a controversy about the authority of Scripture. If millions of years really happened, then the Bible is false and cannot speak with authority on any issue, even the Gospel.
Furthermore, they see their adherence to biblical literalism as essential to salvation. AIG has an interview with the coauthor of The Genesis Flood (1961) John Whitcomb, credited with starting the modern creationist movement;
Dr. Whitcomb then made this pointed application about our need to be concerned for our reputation before God, not men: “Your reputation, your relationship to God in eternity, is dependent on your diligence in handling accurately the word of truth. You don’t just say you believe it, you have to show that it’s true and what it really means. What a challenge!”