In Christianity, many of the old, mainline Protestant denominations are accepting of evolution, gays and lesbians, women, and even atheists. Episcopalians, for example, have women, gay, and atheist clergy. The more conservative groups such as Evangelicals, Pentecostals, Adventists, Mormons, and the like are resisting change, but they will necessarily have to change if they want to be relevant.
I think the two defining issues will be equality, for both women and the GLBT community, and evolution. As the next few generations grow up in these churches and see the “world” treat people with more love and respect than their own church and see the absurdity of a God who would punish someone for wanting intimacy, the more rational and compassionate will continue to leave in increasing numbers. This will leave the churches increasingly weak which would likely further accelerate the exodus. Demanding that women be subservient and GLBT people live loveless, sexless lives based on Iron Age texts just doesn’t fly in today’s world.
The evidence for evolution is already so overwhelming that there is no real scientific opposition to it. But creationist continue to use rhetorical arguments and strawmen based on outdated portions of evolutionary theory to make their attacks. Unfortunately these are effective with a lot of people. Both tactics were utilized in the Issues in Origins class I tool in the seminary five years ago and they were effective for a lot of people. The way the rhetoric works is to make evolution so incompatible with Christian doctrine that people choose salvation over fact. The strawmen tactic is even more sly, you present something that’s been discredited and abandoned by the scientific community using the science that discredited it, the result is much like an inactivated antigen found in a vaccine, just that this inoculates people against science.
The only way that the rhetoric is effective is if people aren’t familiar with or have outright rejected the harmonizing theology of more liberal Christianity, and the strawmen are only effective if you can keep people ignorant of current evolutionary theory. This can continue as long as Evangelicals can bully public school teachers into skipping over evolution in biology classes and Adventist pastors can keep control over their denominational educational system. As long as you keep people ignorant and confused, you can keep them under the control of charismatic leaders.
Fortunately we live in the world of the internet and you can no longer shut out the world. As much misinformation that is available online, there is also a lot of factual information to be found. Most notably, students who’s teachers glaze over evolution can find plenty of science online and those who are convinced that atheists are all a bunch of angry, evil, bitter, depressed communists can find blogs by atheists that prove that we’re actually good people who generally enjoy life.
I think the current trends of teens and young adults leaving religion, especially conservative groups, will continue. Of course, we may see a lot of people just drift towards the more liberal brands of Christianity, but I’d be fine with that. If people want the traditions and ceremonies, then there’s nothing wrong with them having a place to find those. However, I don’t think we will ever lose the fundamentalists. They may become the fringe of society and they may loose political clout, but I highly doubt they will ever completely disappear.