It's very clearly superimposed on pagan festivals and whilst I agree the symbolism is as Christian as Easter, Easter is superimposed on a Pagan festival as well.
"Christmas" is about as Christian as the Easter Bunny, fir trees, chocolate eggs and eating Turkey.
Allowing a seasonal holiday and calling a day Christmas doesn't suddenly create a reality within which non Christians are forced to share their fantasy. Its like declaring a country safe for refugees, or donning a crown and telling the tide to go back to test your Kingship.
Sure, you might get some comfort from dabbling around the edges, but that's on you. Not everyone's comfort levels are the same and the non religious are often seen as fair game for the religious to push around. As we see here, not just in the OP scenario, but in some of the delightful contributions of some of the Christians chipping in.
What it boils down to is that for reasons genuine atheists didn't sign up to they don't get the right to say no, they don't even get the right not to participate or be respected. It peaks on days where Christians don't like to be disobeyed or be made to feel uncomfortable on by the mere prescense of those that dont believe, and can't keep it to themselves.
Taking away people's agency to decide for themselves on matters that affect them has a word. It's a word with a horrible and bloody history and has a unidirectional view of live and let live.
This practising Christian married a non believer, and isn't treating them with due respect. You might in such a situation advise being a doormat, but not everyone wants the boot print on the forehead that comes with.
Ugh.