It is funny how Christians will include any person who says "Jesus" when they hit their thumb with a hammer to get the numbers high enough (2 billion) to beat out the Muslims (1.2 billion) and Hindus (1 billion). If it was just the Protestants or the Catholics, they would be way behind the other big two.
As it is, the number of people in the US who are culturally Christian, ie go to church sometimes and celebrate holidays with their families is pretty high--close to 80% in some states. Religious folks love to cite that as evidence that the religion must be true. All those people can't be wrong. (Although of course, they know that the Amish, Catholics, JW's, Mormons, Adventists and Pentacostals are wrong...)
But when we show the statistics on how the most Christian parts of the country have the worse social statistics, how quickly the no-true-Christian argument pops up. More religion is correlated with more divorce, poverty, unemployment, prison sentences and teen pregnancy? It can't be that religion has a negative effect on social policy. Not at all.
You see, all those people who say they are Christian on forms and such, they are not really Christians. Even if they go to church more often than average, check off on all the important beliefs, pray and tithe and teach Sunday school and sing in the choir. Most people who say they are, are not really Christians. Somehow that 80% shrinks down to almost nothing.
And then they turn right around and say that we atheists should just go to church and read the bible and pray, even though we don't believe in it, because god's goodness will eventually rub off on us and we will start to believe and become good.....