Well, it's the time of year when many Christians in this country become neocon patriots focused on letting everyone know how important Jesus and his daddy are to the creation of our country. (If this generalization doesn't fit you or your situation, please tell me where you live so I can move there.)
What most Christians fail to realize, unsurprisingly, is just how anti-American Jesus actually is.
1) Jesus Is Your "Lord"
When the colonies declared independence from the Kingdom of Great Britain on July 4, 1776, they ceased bowing to lords. And while many people still had "masters", the practice of subjugation was whittled down and stripped away because of the very ideals the nation was found on: the right of every human to seek happiness in life, and to have the necessary liberties needed to attain it.
The Christan religion, however, teaches that Jesus is a master and ultimate overlord to his subjects. This antiquated, small-minded idea is clearly against American values. We are a free people. We have no lords, no masters.
2) Jesus Pervades Everything
With Jesus, it's an all-or-nothing deal. As Bush would say, "Your either with us, or against us". Matthew 12:30 and Luke 11:23 share the same sentiment. This all-consuming approach to your religious ideologies are what drive vehicles like the Religious Right and, more importantly, becomes so pervasive that it starts seeping out into daily life. People in power many decisions based on their religious beliefs (with exceptions, a personal favorite being JFK, who truly understood what it meant to put personal beliefs aside for the bigger picture). But with the tunnel vision such a mind-frame puts you in, it's obvious that if God is your whole life, you'll be spreading it around everywhere you go...and indeed the practice is expressly encouraged.
The founders of America understood this. They had been the subjects of British religious intolerance. They didn't have a choice. They also understood that the only way for all men to be free was to keep the business of governing separate from the business of the church -- from any church. We can't have freedom of religion without having freedom from it, and America's separation of church and state makes that fundamental dream a reality. It's sad and sometimes a little scary to think just how many ignorant citizens are working to change that basic idea. They rant and rave about the men who died to give them liberty and freedom, but then bitch and moan when we want to undo the polarization effects of removing "IN GOD WE TRUST" from our currency or striking "Under GOD" from the allegiance pledge. Do they truly know what "freedom" is?
3) The Ten Commandments vs Founding Documents
Once we get past the argument about which ten commandments are "the" Ten Commandments, we're left with the inane drivel that the nation's laws were derived from these ten lordly decrees. I have a lengthy and perhaps vitriolic post from a few years back that deals with this very issue, so I'll direct you there. Suffice it to say (for those of you who might be skimming these lines between rolls of your eyes) that there are zero "commandments" that became law because they were commandments. The ones that did, such as not killing, did so with stipulations and conditional requirements -- something kingly overseers fail to consider -- and they just happened to be good ideas. But just because a crackhead mentions it's good to put water out for your dog, does that mean you'll let him babysit you kids? Sure, the bible got some things right but that doesn't give it a free pass to scrutiny, nor does it entail some privileged information.
The Christian nation myth will most likely abound right now, just look around. Be sure to check local businesses for signs saying "God Bless America" too. I just saw a local news channel show some redneck blubbering about how the nation was founded on God. Did the "news" station provide any opposition? What do you think?
These were just three reasons, but being free from religion, to me it's clear: the Christian religion -- the one claimed by so many to be the foundation of the United States -- does not secure the blessings of liberty to anyone.