Part of religious conservatives' tactic is to keep repeating the premise that Christmas is necessarily religious. This is important because only if people believe this can they be led to accept the conclusion that an attack upon Christmas is also an attack upon Christianity. If the premise is rejected, however, it is impossible to support the conclusion via that inference.
So little of contemporary Christmas really is religious, though. The most popular and most prominent symbol of Christmas today is Santa Claus, a figure who was arguably religious in his origins but who today completely lacks any religious aspects whatsoever. This has led some Christian groups to renounce any use of Santa in their own religious celebrations of Christmas -- an entirely reasonable decision, given their perspective and values. Some even regard Santa as somewhat Satanic in nature, though that seems rather extreme.
I certainly have no problem with Christians who choose to celebrate Christmas, either as part of their liturgical calendar or simply as a cultural event. The fact that Christmas arguably isn't fundamental to Christianity, and may even be antithetical to aspects of it, does however mean that Christians shouldn't get self-righteous about the way in which contemporary America has drained the holiday of many religious elements. If Christians could drain pagan meanings from it, why can't modern America drain Christian meanings from it?
Indeed, so much of any "religious" meaning has been drained from Christmas in modern America that perhaps it isn't extreme to regard Santa -- the symbol of modern Christmas -- as a bit Satanic. Christmas has become characterized by increased depression, excessive spending, outrageous materialism, troubling debt, ridiculous advertisements, and of course annoying cultural wars over the "meaning" of Christmas itself. If there is going to be any assault on Christmas, it may as well include pointing all this out and perhaps thereby encourage people to chuck it completely.
The above image is taken from a World War I poster depicting a meeting between two devils, one wearing a German army helmet. They are reading a list of all the women, children, and others killed in the past month with one telling the German devil that he's doing good work.