Christmas, Easter and birthdays may well have had pagan links in the distant past but so what?
Christianity has overwritten them and stamped them into the ground, just as many Christian churches were built on ancient pagan sites to crush them out of existence..
Likewise, to their credit the Jehovah's Witnesses built their meeting halls all over heathen Chief Seattles land to delete his tribes pagan beliefs..
So if people refuse to celebrate christmas, easter and birthdays, they're still in a sense being controlled by those long-dead pagan beliefs!