It seems like a can of worms to me. If two groups can have a monument that espouses a view re: religion, then every other existing group should be allowed a monument, including agnostics, satanists, Mormons, Muslims, all different varities of paganism, Zoroastrianism, Sufis, Buddhists, Hindus, each of the varieties of Native American religions, the Church of Monday Night Football (if they still exist), Wiccans, Shakers, Confucianism, and all of the many many others that don’t come to mind at the moment.
Clearly, though fair, and honoring free speech, this would not be practical, thus I propose one and only one Monument for all, an electronic billboard that projects a message for each viewpoint, in succession, with each having an equal time presented. The presentation of each perspective though of equal time would also need to be randomized as to time of day, so that there would not be any lack of fairness in regards to prime times of presentation.
Eventually, there would be so many different viewpoints on the monument, that each would flash by, so quickly that they would be unreadable. Thus it would ultimately become a Monument to the Ludicrous, which, in actuality, is what all of this amounts to anyway. Amen.