This prompted him to make what has become one of the most specious and ill-conceived arguments that has ever emerged from the United States since its founding: that the American way of life, "freedom and all that stuff about the individual, etc. is just a religion like any other".  Ah, that old chestnut... a very popular argument indeed and very widely (apparently even globally) circulated by the likes of Ann Coulter and other great American statesmen like Sean Hannity.   I told my new friend that I wanted to respond to this but that I needed a few minutes to gather my thoughts.  His reply was to say that since I needed to think about my response I couldn't possibly have any conviction of my own about this but was merely trying to memorise an argument taught to me by someone else so that I could regurgitate it. I assured him that this was not the case and began to make my argument, at which time he proposed that we relocate to the bathroom to do a line.  

This was obviously not the proper context in which to argue the fine points of political theory, but I am very certain that the Enlightenment values upon which America's constitution rests do not constitute a 'religion' in anything like the same sense that Christianity does.   No one need ever be rendered silent by such an idiotic claim and I am confident that I can explain the difference.

First, the Coulter claim (i.e. "Your liberal values are a religion too!"), even IF it were true, is a fallacious form of argument.
Here's an explanation:

Tu Quoque is a very common fallacy in which one attempts to defend oneself or another from criticism by turning the critique back against the accuser. This is a classic Red Herring since whether the accuser is guilty of the same, or a similar, wrong is irrelevant to the truth of the original charge. However, as a diversionary tactic, Tu Quoque can be very effective, since the accuser is put on the defensive, and frequently feels compelled to defend against the accusation.

Source:

S. Morris Engel, With Good Reason: An Introduction to Informal Fallacies (Fifth Edition) (St. Martin's, 1994), pp. 204-206.
http://www.fallacyfiles.org/tuquoque.html

But fallacies aside, it is simply not true that there is anything analogous between Christianity and the liberal founding values of the Enlightenment that are enshrined in America's constitution.  Christianity dictates a definition of "the good life" for all of humanity, while liberalism establishes the conditions under which individuals may define and pursue their own definition of "the good life."

Christianity (as the Republican right understand it) is inherently authoritarian, theocratic (anti-democratic) and assumes that "moral agency" just means obedience to external authorities who punish those who do not obey and reward those who do.  The very reason why our founding fathers prized freedom so highly was in order to make moral agency a serious possibility.  Where there is no freedom (i.e. no possibility of vice) nor can there be any virtue. In order for moral agency to be possible, one has to be free to choose it, not out of a prudent, and selfish, desire to save oneself from punishment, but from a genuine will to do the right thing. America's founders understood, quite rightly, that there is a difference between selfishness and morality.  Indeed, intuitively, we all know that being good is something different from seeking pleasure and avoiding pain -- the latter are merely animal instincts, not virtues that warrant praise.  Liberalism marks out a sphere of individual sovereignty precisely so that the agent can pursue his own convictions and his own vision of the good life (within the limits of the harm principle).  If an agent is merely performing in an obedient manner to avoid the censure of external authority figures, this does not make him worthy of moral praise, it merely makes him a clever and prudent actor.  

I hope this puts the "church of liberalism" fallacy to rest, once and for all.