There are two basic points to make about tolerance as a civic virtue. The first is logical and the second historical.
The logical point is that tolerance cannot be a free-floating virtue. This is because no virtue (or vice either) can be found in a transitive verb. It is not a matter of whether you tolerate, for everyone does, but rather a matter of what you tolerate.
If we were to say that Smith tolerates x, we do not yet know if Smith is a hero or a skunk. Does he tolerate respectable dissent, responsibly offered? Child porn? Smokers in bars? Transfats in restaurants? Ethnic violance? What does he tolerate? This is what Rushdoony used to call an inescapable concept -- not whether, but which. As soon as a man shows his hand, and we know what he tolerates, he is put in a position where he cannot tolerate those who refuse to tolerate what he does. A wide acceptance of the homosexual agenda, for example, means that a society has to crack down on the "homophobes." Not whether, but which.
This leads to the question of what a "mere Christendom" would tolerate. Every organized society excludes certain behaviors by definition, and is inclusive of others. This is what it means to be a society. Every society has shared values, and it polices those values. When those values are not policed, you have a condition of anarchy, or what the older civic theorists used to call "a state of nature."
This being the case, it is certainly appropriate for people to ask what a member nation of this mere Christendom would tolerate, and what it would not. For those who gain their information about such things from the screechings of the alarmist left, the answer will perhaps be surprising.
Christians invented the most open and tolerant society in the history of the world. Tolerance, as we have known it historically, is a Christian virtue. As preachers of the gospel spread throughout a society, and new life comes to more and more of the population, the preconditions for an open society are being established. The more the law of God is written on hearts and minds, which is what happens under the new covenant, the less necessary it is to have standards of public decency urged upon us from billboards. There were all sorts of things which, prior to the last several generations of general deterioration, "went without saying." Once that consensus is gone, you have to start calling the cops for more and more situations, and freedom starts to erode.
Now some might say in protest that they are quite certain that if evangelical Christians had their way, there would be no more acts of simulated copulation on parade floats in San Francisco, which is quite true. The observer would go on to point that that such open behavior would not fly in the totalitarian hellhole that we call North Korea, and QED. But they fail to note that such frank displays of deranged yearnings would not have flown in America in 1958 either, which was a truly open and free society. All freedom necessitates restraint and, for those who have been following this, the question has to do with who is restrained, and how.
An important part of the how concerns not the identity of those restrained, but their position in that society. This will have to be discussed further in its place, but are those being restrained at the center of that society, or are they outliers? Is the standard enforced with fines ten times a day, or twice every ten years?
Free societies can only function when the authority of restraint is found in the old fashioned virtues of self-restraint and self-control. Free governments presuppose self-government. This is why John Adams said that our Constitution presupposes a moral and religious people -- it is, he said, "wholly unfit for any other." And it is wholly unfit for any other.
All this said, it remains an ineradicable part of the historical record that free societies arose and grew out of Christian societies. I am arguing that there is a connection, and that this is not mere coincedence. I am arguing for a return to the preconditions of civic freedom, and am not arguing for an abandonment of them. Unbelief does not generate free societies. Out of all the explicitly atheistic societies that formed over the course of the last century, how many of them were open and free societies? Ah . . .
For secularists to treat believing Christians as the principle threat to their freedoms would be, were it not so serious, not very serious. But that goes without saying.
So as I envision it, a mere Christendom that would provide more real freedoms for the unbeliever than the current unbelieving society grants to believers. Measured by the Golden Rule, when we evaluate our respective proposals, they have far less to worry about than I do.
But for some, it all comes down to sex. They want to keep the government "out of our bedrooms." What are they talking about? I have to live in their society, remember. And I built my house, which means I built my bedroom. The government told me how far apart the studs had to be in my bedroom wall, they dictated how thick the sheetrock had to be, they mandated how far apart the sheetrock screws had to be, they had policies on the configuration of those sheetrock screws, they have laws on the size of the windows, what kind of glass I can have in them, and there are stern legal warnings on the mattress tags. What do you mean, you want to keep the government out of our bedrooms. The president is probably contemplating, right this minute, the establishment of a bedroom czar. And when he does, the usual suspects will be out there on the Sunday morning talk shows, defending it. This is because secularists don't know what real freedom is. Their worldview doesn't have a slot for it.