If all faiths are given the chance, public displays of faith are constitutionally acceptable.

"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof" The establishment clause of the first amendment does not say that Congress shall make law such that it respects all establishment of religions equally. It says that Congress shall make no law respecting an establishment of religion. Pluralism doesn't fix this problem. These are still "displays of faith" and it is the duty of the United States government to treat all people equally, myself included. I am an atheist. I have no faith. I can make no display of faith. I can make a display certainly, but not a display of faith. And that's the rub. If the government offers a public space to first-come to put up a display they are perfectly permitted to do that. However, if they ask for a "display of faith" they have stepped over the line. As for your claim that the SoCS doesn't expressly prohibit the states from such action, there is certainly an argument to be made there. In fact, Justice Thomas has expressed an affinity for the argument that if a state wanted to declare a state religion that the first amendment wouldn't prohibit that the law refer only to congress. However, outside of crazy arguments the 14th amendment to the constitution holds the constitution applies to the states and such argument cannot stand. The constitution does not expressly or implicitly prohibit religious displays on public property. It simply cannot judge them as a subcategory. For example, if the government offers a space to be reserved to people meeting certain criteria (usually no profanity, proper insurance, nothing dangerous) to put up a display on public property they can no more suggest that a church take this space than a book club, free-thought group, or even a company to plaster it with ads. It isn't that you need to offer the space to simply ever faith you need to offer the space to all groups and individuals without any consideration if they are religious or not. You seem to be under the mistaken impression that opening a space for a "public display of faith" to atheists is a coherent notion; it isn't. This careful middleground approach is inherently a religious approach. You are quite clearly trying to suggest a way in which offering it to all religions makes it somehow not religious. Should areas be available to everybody by reservation, certainly, they are public property and should be available to the public. However you can't simply offer this to the religious public, you need to offer it to the entire public. Secondly, let me note a quick a secondary problem with this argument. It doesn't work in practice. For example, such an offer was taken up by the AAI (an atheist group) to put up a display called "Tree of Knowledge" including books and other such items. Although permitted, a number of people made a very big deal out of it. People argued that although they believed in free speech that atheists shouldn't have the temerity to express such a right. Another display in a different area was put up by a local Wiccan group was destroyed as somebody ran it over during the night. Being inclusive is often a rallying cry to privilege Christianity. You can offer the space to all faiths, and you'll just get a couple church displays and verbal, physical, and destructive abuse to anybody else who tries to take you up on the offer. In short, you can't, as the government, ask for "displays of faith". When governments do do this, they really mean 'displays of Christian faith' and in practice that is what they get. Allowing groups to make a display in a public place is fine, allow that group and those displays to be religious is fine. Asking if somebody wants to put up a display of faith in the three weeks before Christmas and oh, other faiths can put up displays but we'll destroy them and yell at you if you do, is not allowed by the establishment clause. There's a line, and this suggestion is still on the wrong side.