It's insteresting that you posted that site. I read about where 93% are religious but it never did indicate what religions. Since the U.S. is abundant with differing religions, it does not pin point to any number of them being Christians.
But lets just say that the majority are Christians. The Holy Bible does not teach such practice and in fact it is sin because it's a sexual act that is not under the convenant of marriage.
1 Corinthians 6:18 (NIV) further confirms this, saying that unlawful sexual relations defile our own bodies. "Flee from sexual immorality. All other sins a man commits are outside his body, but he who sins sexually sins against his own body."
If one claims to be a Christian and yet commits such act knowingly, then he is sinning against God. The Holy Bible does not commit the act. God does not commit the act. Instead, man and his sinful nature commits the act. This also applies to sex outside of marriages, masturbation and lusting..."You have heard that it was said, 'Do not commit adultery.' But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart" [Matthew 5:28].