No its not JUST a Christian holiday - no matter its disputed origins, it is also a national public holiday. In the UK it and Boxing Day are both Public Holidays, in the USA Christmas IS a Federal Public Holiday:
http://www.opm.gov/Operating_Status_...edhol/2012.asp
Some may celebrate religion, but its still a national Public Holiday that has entirely secular celebrations around it as well as the religious ones. You may be over-sensitive and refuse to observe it, but that'd be like me going to the USA and refusing to observe Fourth of July. Or Khen going and being upset by Veterans Day.