Have you ever read or watch the play "A Man for all Seasons?"
Imagine if you will, Hindu's take over this country, they start saying that it was Shiva's (or whatever their "god" is named) goal to bring Hindu's to America and because of that America is a Hindu country. And they start by changing under God to Under Shiva. How would you feel?
I am confident in my Christianity, if we keep pushing our Religion down the throats non-christians (yes, they are wrong, and probably going to hell, but there is nothing we can do about it other than set a good example), we are no better than the Mullahs of Iran.
There is nothing at all wrong with a society whose members are overwhelmingly adherents to a particular religion to establish national holidays for all to observe. Those who are non-adherents can respectfully rest and reflect and recreate in their own ways if they wish to. No one is being forced to offer worship or praise in any particular fashion.