You have to realize that Christmas has lots of meanings for people that have nothing to do with its religious significance. Many, many non-Christian people celebrate Christmas for all kinds of reasons: tradition, family, togetherness...presents... So you have to ask yourself, does the person belong to another religion with their own holiday? Or are they just not a practicing Christian but still willing to take part in all the Christmas goings-on?
If you want to be safe, send cards with a more general message: "season's greetings" or "happy holidays" or something. Those apply to people of other religions who have their own holidays around the same time, and they're appropriate for atheists, too. Or just send out your normal "Merry Christmas" cards.
If you like someone well enough to send them a card, I would hope they're not going to get bent out of shape because you're wishing them well. "Merry Christmas" is a common enough sentiment that most people aren't going to take offense, no matter what their religious beliefs.
It's because the celebration of both Christmas and the use of the tree was not religious in the first place (well not Christian anyway). We all know Christ was not actually born on December 25th. It was a pagan holy day that was imported into our culture into an effort to gain more followers (not the best practice of course).
Worshipping on Sunday instead of Sabbath was instituted for the same reason. But most people don't know that so is it impolite to push pagan tree worship that was stolen by religion onto non-believers? Technically yes since we stole it from them to begin with.
Enjoy explaining that one in your cards - could be fun. But people that celebrate Halloween don't delve into the origins of the holiday any more than people who celebrate Christmas do so what it boils down to is are you trying to witness to your non-believer friends? Or enjoy Christmas?
If you are witnessing, do it on a day other than Christmas and your concern about etiquette is resolved. If you just want to enjoy the holiday and celebrate it with your friends, do it without a Christian card. There are plenty out there to choose from.
Christmas has become more about tolerance, accepting people and commercialism than Christ these days. So people having trees and decorating them is about family and friends, that's all. Depending on where you look (and whose interpretation of history you choose to believe) you will find different explanations for the origins of Christmas.
I've linked two sources below - be forewarned that they disagree in some ways. But they might be an interesting place to begin a deeper study if you're interested. Never take anyone's word for what is in the Bible and always research your sources (even ones that agree with your point of view).
Never blindly follow something just because it makes sense today or already agrees with you. :) Oh, and Merry Christmas!
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.