Looking at all the religious oligarchies around the world I am thankful that the U.S. is not a Christian nation. Without exception those countries that adhere to a strict religious dogma are plagued with strife, war, and are constantly battling with their neighbors.
I am totally convinced that the reason that the U.S. is what it is today because of our diversity. We are a nation of immigrants from hundreds of countries and religious beliefs. I can easily see that the diversity level in the blue States is glaringly higher than in most red States. Maybe this accounts for some of the more fundamentalist attitudes among those in those parts of the country.
I grew up in a rural area in the very red State of Indiana and was therefore never exposed to our diversity until I went to college. Part of my rural Indiana heritage in the 1950s and 60s was also being exposed to the local chapter of Klu Klux Klan. My dad kept very much away from those folks and demand that I do the same but we did see the cross burning on occasion out west of our small town. To me the KKK is somewhat representative of what our country might at least to some degree be like if we were a Christian nation.
Several of the original thirteen colonies were established on various religious groups. There was very little tolerance for anyone in those colonies for people of different religious beliefs. Some even imposed a death penalty for trying to convert its citizens to your brand of religion. Thank heavens they had to shed any of those remaining beliefs before they were allowed to join the union. We are the nation we are because we have celebrated our differences instead of always fighting each other because of them. I hope we never forget that basic fact.