It seems to me that this topic is a lot of talk about nothing. Whether one says Merry Christmas, Happy Holiday, Happy Hanukah,Happy Kwanzaa or something else along this line it is a greeting or pleasantry that should be answered in kind. I usually say Merry Christmas but will use Happy Holiday or Happy Hanukah (if I know the person is Jewish) and use the greetings interchangeably. It is not meant as an insult to anybody. It is just a seasonal greeting. I certainly do not ask anyone their religion or ethnic background before greeting them. What I do object to is anyone telling me what I should or should not use as the seasonal greeting at all times.
TK