(No link, because I don't want to accidentally create a dog pile.)
As it turns out, I somewhat mistook the context of my friend's remark, but I still wanted to repost what I said, because I think it may have some value. Below is a synthesis of several comments of my own:
I think you're oversimplifying terribly. I don't know a single liberal or atheist who doesn't believe firmly in the social contract, and the social contract requires rules. Frankly, from our point of view, it's conservatives who have been abandoning the rules in working so hard over these past decades to void much of the social contract.
As an atheist myself, and definitely a proud refugee from religion, I write about religion all the time in my fiction. See my entire Mainspring series, as well as my Green series, as well as a large percentage of my short stories, as well as Death of a Starship, whose protagonist is an Orthodox priest, and my yet-unpublished Sunspin, one of whose key characters is also a Christian priest. Portrayed with loving care and as much internal honesty and morality as I can manage, not with liberal snark.
To oversimplify on my part, the fundamental disagreement you're so casually alluding to isn't over the question of rules vs. no rules, it's over the source and meaning of the rules. I don't think any single faith should be the source of societal rules. How would you as a conservative Christian feel about living in a society based on rules drawn from the Sharia, for example? That's how I feel about living under Christian rules. Though in all fairness, the vast majority of the secular rules I favor and the Christian rules I presume you favor are in alignment.
In my personal case, I have a particular allergy to both Evangelicalism and Fundamentalism, but I also work pretty hard to talk about religion fairly in my writing. I'm an atheist, but I'm not a fool, and religion is one of the defining human experiences/institutions.
Likewise, on the political front, the assertion that the US is a Christian nation is obvious religious fantasy when contrasted with the blackletter content of the Constitution as well as the writings of the Founders taken as a whole in context (as opposed to cherry picking 'gotcha' quotes). Nonetheless, it is an act of intellectual idiocy to deny that we are overwhelmingly a Christian nation in a cultural and historical sense. To me, freedom of religion means freedom from religion. That in turn is the single most important protection any particular religion or denomination or sect or individual faith-holder has in pursuit of their own religious freedoms.
To sum up, those of us who reject religion in our own lives are not the libertine1 anarchists of conservative fantasies. We're just people who think there are better ways than arbitrary faith in revelation to organize society. Better for everyone, including faith holders.
1. Well, okay, I personally am something of a libertine, but that's not the point here.