When considering that the U.S. religious reality is a marketplace of faith and ideas, it’s easy to think that it becomes a competition. ...Steve's describing exactly the sort of interfaith relations that are key to a functional, multicultural, democratic society. But the thing about marketplaces is that everyone has to more or less agree on the rules that govern them. For different religious positions (including non-religion) to take part in a marketplace of faiths, every one has to consent to a certain level of mutual respect and civility, and everyone has to agree on some set of universal "goods" by which competing religions are measured. The separation of church and state is supposed to enforce exactly this idea - regardless of who is in the majority, be they Christian, Hindu, atheist, or whatever, society still works by a set of rules that everyone recognizes as good.
But the marketplace also invites creativity, not just competition. I think of the markets of Morocco or the shops at Reading Terminal Market in Philadelphia. Sure, what’s offered is largely the same — clothing, art, food — but it nourishes differently and uniquely.
But I don't know how many religious people are interested in playing by a set of common marketplace rules. To do so is to admit that there are some overarching ethical principles that are held in common by people with all faith positions - and that these common principles are more important to the way society works than the special revelation of any one faith or denomination. That's directly opposed to the claims of most religions (and anti-religions), who are more interested in establishing a monopoly than trading ideas in the marketplace.