But what if that person is an agnostic or an athiest? People with a religious belief system (in this case christians), don't have the market cornered on peace, love, good will, etc.
I don't wish to start a debate - certainly not on this thread, but if a person extends a greeting to you, why not just accept it, and don't expect them to see the "big picture" just the way you do.
After all, there aren't really any holy days, they don't exist, no matter what religion, they exist on a man-made calendar only due to the importance that we place on them.
Wednesdays don't really exist in nature, we just call it that because we need a point of reference.