I don't have any problem with celebrating our pagan background. It is part of my ethnicity as a "European American". Christmas trees, Easter bunnies, yule logs, Halloween costumes, jack-o-lanterns, they all make us who we are.
But Christmas trees, Hallowe'en costumes, jack-o-lanterns, etc., are not celebrations of our pagan background. They are fully Christianized traditions now, incorporated into the symbology of the Church. They were once pagan, but they are not longer, and when we use these symbols on holidays, when we understand what we are doing anyway, we are in no sense returning to our pagan roots. Those roots may have inspired the rituals originally, but they've been "Baptized" so to speak, and are now Christian. In truth, most of these things have been Christian now far longer than they were pagan before that.