In the US, not only is Catholicism declining, but so is Protestantism. Huge numbers of mainline denominational churches have closed; those that remain have very few young people. There are a few mega churches, but keep in mind dozens of small churches closed to make this one big church possible. But the mega churches near me seem to have very, very little doctrine of any kind.
Some formerly reliable evangelical churches, such as Baptists, are sliding towards the mainline on issues like abortion and same sex marriage.
Some people go to non denominationals for the weight loss class, others for the addictions support group, still others because they like the music, crafts, or the family activities. They remind me of the YMCA, with a religious service added in. Listen to Joel Osteen for a half hour: There is nothing anyone would disagree with, but also hardly anything specifically Christian. The mega churches near me seem to be community centers, so for most of their adherents are not really contact with Protestantism.
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