It's all about anything remotely connected to someone else's sexual sin, whether it's infidelity, premarital sex, pornography, abortion, homosexuality, sexual deviancy or whatever. It's as if sexual sin is judged a far greater transgression than disobedience to other commandments and teachings.
How else could so-called right-to-lifers roundly condemn abortion and then support the death penalty? What else could cause them to gauge personal morality solely on the basis of sexual behavior?
George Bush knows this, and he cynically uses it to keep evangelicals in lock-step behind his candidacy, each time headlines threaten to cause them to see the bigger picture. He touts a Same-Sex Marriage Ban Amendment to the US Constituton not because it will succeed.....the votes clearly aren't there for passage....but to emotionally manipulate evangelicals, rather like using irresistible bait to catch fish.
Jesus spent very little of His earthly ministry teaching about sexual behavior, and only one of the Ten Commandments directly deals with sexual sin. It will be a great and joyful day for God and His people when Christians start focusing on His priorities and the Good News, and stop investing far too much energy on certain specific sins, to the detriment of all other teachings.
Obsession with sexual sin to the exclusion of other Godly concerns is precisely what drives people away from evangelical churches.