It's amazing how emotions and bias get in the way of reasoning so quickly.
1) Banning Christmas because it's a birthday is stupid. I have stated many times here I see no scriptural basis for the ban on birthday celebrations.
2) The pagan-origin reason is crap as many of you have well pointed.
3) The World-is controlled-by-Satan reason is also BS (By that token JW's shouldn't watch the SuperBowl or the World Cup, or watch TV)
But my reason for not celebrating Christmas is not that it's a birthday, or pagan or worldly: It's because Jesus WAS NOT born on Dec 25th. Period! The reason behind Christmas is Jesus' birth. If you don't believe the Bible, why would you want to celebrate his birth? And if you do accept the Bible you have to admit he was not born on such date.
I'm no JW apologist (hard to swallow, i know, since I'm an active JW), but I think JW's have a solid, reasonable cause for not celebrating christmas. But by giving lame, weak and stupid reasons (like the three I listed above) WTS has weakened the real reason.