We are being forced to face the question head-on. And we (SCOTUS) should say that we are generally a Judeo-Christian nation and not a Muslim one.
Although maybe it can be avoided in the case of monuments, because one of the good things about Islam is that it doesn't build monuments (well, except for minarets, so maybe that's a half-truth.) So this Christian monument on public land could be allowed without risking Muslim monuments appearing under protection of the ruling.