In spite of your desire for an American Monoculture (TM), diversity of thought is actually on the rise here. Recent surveys show that practicing Christians are approaching a minority status in this country. You may see this as a sign of the end of times, but I disagree. I don't care whether people have faith in an unprovable deity or not, but I do appreciate seeing more diversity in thought.
In defense of d_r's viewpoint, there may be some (or even a huge chunk of people) who adhere to some notion of a "Christian Ummah". After the Second Coming of Christ (soon, please) we may arrive near there, I suppose. However, short of such an unambiguous, global, history-making-a-sharp-turn event, the whole notion's a wash.
In me, you have a specimen of what Marxist Hacker 42 might call sola scriptura fundamentalism, though I really don't consider myself "Protestant" in that sense. It's possibly to cheer the Pope when he's Biblically on point, and fade when he drifts (in my opinion) into arbitrary tradition.
Ultimately, there is the individual, and there is the Almighty. God will remain "unprovable" at an intellectual level while we're here under the sun, before the Second Coming. Why, you ask? Not claiming to speak for God, but it sure seems, that all individual specimens of mankind must be on the hook for what they do or leave undone with the information given them about What Life Means.
Thus, "diversity in thought", itself, is a kind of a bugaboo. But who can deny that it's a shiny one for the fallen mind? Are you really after more noise in the signal? Do you really want more illness with your health? Hangovers with sobriety? Truly, everybody has to explore truth and falsehood on their own, but it seems that the basic objects of male, female, family, right & wrong don't have much deviation across the human experience. One seeks "diversity of thought" to roughly the extent one mixes buggy functions into the final code release.
But let's go after a kind of diversity. A Venn diagram of various faiths indicates substantial overlap. It's more fun to rejoice in the commonality of faiths than it is to spend time thumb-wrestling on whether zippers are sinful and buttons are the only proper closure for clothing. To me, "diversity" means that we don't run around thrashing each other on fine points of Calvinism vs. Arminianism, and we certainly don't waste time trying to regulate morality via legislation (Roman Epistle). On Tuesday, I had lunch with a Muslim fellow at my company, and shared with him the plot for a "boy meets girl in Afghanistan" novel I'm working on. It's important to capture the Islamic faith of the girl in a way that's accurate and educational for the reader, and doesn't bring a fatwah down on my head. Osama is actually a cool chap, and I'm blessed that the Almighty arranged for him to be my church deacon's next door neighbor, and work at my company.
Back on topic: that which is proper, pleasing, useful, and consistent over time is far from "new". Only technology has varied, not human nature. If you think "diversity" == "velcro genitals" and the Sexual Geometry of the Week Club, I only ask that I be excused, and the right to protect my children from such confusion in their formative years. Once they have a foundation in good vs. evil, I can only pray that my teaching guides them toward the former.
To summarize: your criticism has substantial basis, but is by no means the whole of the conversation.