Kevin Drum has a few smart thoughts on why conservative Christians might feel persecuted in a country that overwhelming identifies as Christian:

A century ago, something like 10% of the country belonged to a conservative Protestant denomination. That's grown steadily ever since, and today it's around 30%. So there's really no mystery to explain here. Conservative Christians have become more outspoken and more politically powerful simply because they've grown more numerous. Sometime in the 70s, their numbers finally passed a threshold where they became a serious voting bloc, and they've been growing more powerful every year since then. We've been chipping away at traditional religious expression in the public square for decades. At the same time, conservative Christians denominations have grown steadily. Put the two together and you have a substantial segment of the population that feels like it's under assault.

I would add one more thing, namely, the rise of an evangelical subsculture. A significant number of conservative Christians-and evangelicals in particular-live in tightly sealed communities that cater exclusively to their beliefs and values. Indeed, a substantial number had lives like this:

You're homeschooled-with a heavy assist from your church-you attend evangelical retreats, you listen to evangelical pop music, you watch evangelical movies, you go to evangelical social events, and after you graduate from your evangelical private school, you go to a Bible College or evangelical university. From there, you get your secondary degree from another evangelical school, and you eventually settle in an evangelical community.

This is simplified, but it isn't exaggerated; a substantial number of evangelicals live their lives in a bubble is isolated from the overwhelming secularism of mainstream culture. It's no wonder that those who leave the bubble are shocked and feel assaulted; the world they see is vastly different from the one they came from, and that's scary.