[Based on 40+ years of dealing with creationism…]
It doesn’t make sense to an enlightened Christian, which is why you need to visit the hard right sites. There are Christians who care what Christ taught, and those who make God in their own angry image. To those folks, the Bible means that if you can justify something in the Bible, you are free to write off any factual evidence, logic, alternative interpretations, or humanitarian appeals. In fact, the very fact that those things disagree with the Bible proves they are wrong.
People who talk about “imposing beliefs” on others show how much they miss the point. To the hard-core believers, there are no “beliefs.” They regard the evil of abortion or homosexuality as documented facts, as demonstrated as the Battle of Gettysburg. The fact that other people reject their document is not their problem. They consider cracking down on gays or abortion as entirely equivalent to the FDA cracking down on a quack cancer cure, an action completely justified by documented facts.
They don’t care beans about evolution or the age of the earth. They care only because the science on those topics undermines the notion that every single word in the Bible is literally inerrant. There are 37,000 verses in the Bible. Proving all of them true is a tall order (we’ll cut some slack on “Jesus wept.”)but if you can sell the idea that the Bible is true in toto, then, “The Bible said it, I believe it, that settles it.”
If you talk to most of these people individually, they are very nice. They might say gays are bound for hell, but they’ll be courteous to actual gays they meet. The real evil comes from the leaders, the people you see being quoted on Right Wing Watch. But they’ve sold a lot of the flock that real Voldemorts are out there needing to be fought.