Without that basis, the moral glue that binds our diverse civilization will crack, and moral chaos will ensue. The weakening of Judeo-Christian values makes America a less moral place, and one more hospitable to hate groups. When moral norms break down, Jewish security will erode. When American Jews reflexively oppose any public affirmation of Christianity, they weaken their fellow Americans' attachment not only to Christian values, but to Jewish ones as well. God-based moral law.
Tolerance is important, but it's insufficient as a moral guide.
The emptiness of tolerance and diversity becomes clear when we consider the question of anti-Semitism. The problem with Jew-haters is not that they are intolerant and don't care for diversity. To keep replaying the mantra of tolerance and diversity is to avoid confronting an evil that far transcends intolerance. Intolerance of diversity explains why gentiles once barred Jews from country clubs or devised quotas to limit the admission of Jews into universities. Such acts were surely bigoted, but real anti-Semitism is simply evil.