I don't know what most of the arguments going on here are about, but am I the only one who is more proud of my religion for what it has done uplift humanity and connect us with God than with any of this other stuff? Any religious belief or non-religious belief can inspire a person to write a piece of music, build a building, or even found a country, but I am proud of the particularly Christian versions of these things precisely because they are Christian versions, and hence they are meant to inspire people to connect with God and transform their lives in Him by repentance, fasting, and prayer (I am assuming that on a Christian messageboard I will not have to explain why this is a good thing!). I guess in that sense I am a 'Christian supremacist', though I also recognize that this isn't anything that the followers of other religions couldn't also say of their own music, buildings, and countries. (And, yes, while people may debate just how much we can call the USA in particular a Christian nation, there are other nations for which the founding of their churches are much more plainly and obviously tied to their concept of nationhood or peoplehood, e.g., Armenians are generally very, very proud to hail from what history shows us was the first Christian nation, and particularly against the backdrop of the surrounding eventually Chalcedonian and Muslim states, they are right that they are inheritors of a unique heritage via their Church, though I doubt even they would say that this means that Armenian Apostolic Christians should be preferred in the nation's law code...if it's actually like that over there that'd probably be because they are well over 90% of the entire society, which is not the case with America and any of its Christianities.)
It just seems that out of all the things that you could say about Christianity, "Christians founded America" is one of the more contentious and potentially negative things to focus on. I think there are better, more edifying things to focus on, and that the more we focus on them instead of wistfully talking about the past (a past which never existed outside of certain people's heads), the less we'll need to have these arguments, or to consider religiously-biased laws to protect people who apparently can't protect their communities against possible demographic shifts.