This is not the gotcha to Christians that some people seem to think it is. My children were taught in Catholic Sunday school that no-one knows what time of year Jesus was actually born, but we celebrate his birthday during the darkest time of the year for us because it brings us hope.
I remember there was a thread on AIBU at Easter about people not really celebrating anything apart from chocolate eggs, and about 30+ different people posted variations on "but didn't you know that Easter is just the Christians ripping off Ostara?"
Well (1) yes, Christians do obviously know that Jesus didn't invent Christmas trees or the Easter bunny, but also (2) lots of the things that atheists and neopagans seem to assume are the authentic, or original, festivals, were at least collated and rationalised (and possibly invented/embellished) in the last 200 years or so, again often by men.
Just use this time, when most people thankfully get a few days to slow down, to celebrate what seems important and true to you, in your own tradition. Someone higher up the thread said they celebrate consumerism, which sounds absolutely miserable to me; but then someone else said they'd be bored to tears in church so my Christmas would probably be miserable to them.