It is indeed and truly an eye roller when someone tries the, "well you realize Jesus wasn't born on December 25, don't you?
As if they are in possession of a bright and shiny fact the likes of which was never been seen before.
After restoring my own eyesight, I invariably launch in to a bright and chipper lecture about how <i>clever</i> the early church was in culturally appropriating the hell out of pagan festivals. Since an annual festival is the last thing a local culture will willing give up.
They would invent a new holy day and plant smack on top of the pagan festival and not freak out about the original meaning of Christmas Trees and (*shudder*) candy canes. The early church fathers were quite correct in assuming the original meaning in the symbolism would be completely forgotten.
The Christ Mass was never meant to be a happy birthday dear Jesus party or (entirely) paper over various midwinter feasts.
It was meant to celebrate the birth of God's Son. The birth of hope.
(Sorry Mrs Wiley you were a sweet but theologically dangerous silly old Lady)