While I find your point about Christians founding this country, so we should all be christian, bullshit (Yeah, I know that's not what you said, but close enough), I WILL agree that "Happy Holidays" seems so non-committal and soft.
I don't know about any of other holidays besides Christmas and Chanukkah, so I can't comment on that. But what I WILL say is the Chanukkah is the biggest bullshit holiday and LEAST important holiday in the Jewish Calendar. So with that, as a Jew, I say Merry Christmas, because in my mind it is the only really important holiday occurring this time of the year.
That being said, if I'm speaking to a middle-eastern family or Hindu person, of course I'll offer a more generic salutation, but if I'm stumbling through Biloxi and go to buy a water from the gas station, I'll merrily say my farewells to Bubba with a "Merry Christmas!"
So may I offer all Christians on this board a very hearty, and Jewish, "MERRY CHRISTMAS!"