Personal beliefs are, and should be, just that: Personal. There are enough opportunities for people to express their personal beliefs in the privacy of their homes or in their respective places of worship where, I believe, they belong and are more appropriately expressed.
There are many "core parts" of people's lives which do not warrant a public celebration in a government building or school.
Homosexuality, for one. I'm sure you would agree with me that a huge banner celebrating Gay Pride Week would not be appropriate in a government building or a school.
And it's not about what the majority of people want or believe. As I've said on a number of occasions, democracy is not necessarily about "Majority Rules" at all times.
And even if it is, I'm not convinced that prayer in schools or nativity displays in government buildings is what the majority really wants.
Sure, I'll agree that the majority of Americans are religionists, but it does not necessarily follow that they agree with your position.
Anyway, I have to go take my blood pressure medication now......