Although this is a common question this time of year, the answer is quite simple.
There is no legitimate scriptural reason not to celebrate Christmas. At the same time, there is no biblical mandate to celebrate it either. In the end, of course, whether or not to celebrate Christmas is a personal decision. Whatever Christians decide to do regarding Christmas, their views should not be used as a club with which to beat down or denigrate those with opposing views, nor should either view be used as a badge of honor inducing pride over celebrating or not celebrating. As in all things, we seek wisdom from Him who gives it liberally to all who ask (James 1:5) and accept one another in Christian love and grace, regardless of our views on Christmas.