All over America it used to be people would routinely greet eachother with 'merry christmas' decades ago. It was a joyous expression that people willingly shared. Even jewish people and other non-christians were happy about it and shared in this greeting. It was not disrespectful towards non-christians at all to say merry christmas. Today there is a very strong effort to get these habits out of the American people.
Merry Christmas anyway.