I don't know if I'd go so far to say that it is "un-American" but there is a lot of evidence to suggest that the notion of American being a "Christian Nation" runs counter to the Founding Fathers intentions.
The term "separation of church and state" derives from a letter written to the Danbury Baptists of Connecticut explaining to them that they should have no fear that the gov't would institute a national religion.
When they try to impose religious based laws over people of different beliefs it is unconstitutional and when they claim authority from belief over that of the constitution it is un-American.
My take is that colonial Americans certainly mostly were religious, specifically Christian as it was a custom past down from its European past, but that the government itself sought to remain completely neutral. Therefore the invocation of the US being a "Christian Nation" is prefaced on a distortion of the facts.
Agreed. They were all well acquainted with the excesses of theistic governments, including the burnings, torture and executions of people not of the "proper" faith -- even including other Christian sects. Including those very same behaviors in Massachusetts by the Puritans in spite of them coming to America to escape such persecution. Shoe on the other foot is just as evil.
Christians should be happy here, and they should embrace full separation of Church and State. That they aren't is their fault and their narrow-mindedness.
Not only is it delusional, it is dangerous: who gets to decide which particular sect's beliefs will be ensconced and who will determine what punishments are meted out for blasphemies against those beliefs?
There's a Youtube channel called "Knowing Better" that is well worth checking out. A recent video covered the Sovereign movement, which is more or less the fringe of the Ron Paul movement (uber-fringey). One subset of the movement claims that they aren't subject to US law because the government is not God. Absolutely amazing.