100 years ago most Americans were Christian...?
Today most Americans are Christian. 100 years ago most folks in the Middle East were Muslim. Today most Middle Easterners are Muslim. 100 years ago most Indians were Hindu. Today most Indians are Hindu.
Theists, why do you claim your brand of religion is true, when it is obvious that religions are passed down like traditions in a society? Most people end up believing whatever their family or society believes in (if this were not the case, America would be mostly Christian one decade, and perhaps mostly Buddhist the next, pagan the next).
1000 years ago, everyone believed the earth was flat. Did that mean it wasn't round?
Whether knowledge of something is passed down in society or not, it doesn't have bearing on its truth.
100 years ago most Americans pretended to be Christian ...
Why would inherited beliefs be any less true than something that people came up with all on their own?