When i was a JW my reply was:
We follow the bible. If you read the bible and dont add to it you'd come out with our religion. Christmas isn't in there so we dont do it. There's no pope, there's no trinity, there's no hell. And we preach because that's what Jesus did when he was on earth. We immitate Christ.
Oh how blind i was. 1914 isn't in there, shun isn't in there, disfellowship isnt in there, judicial committee isn't in there, organization isn't in there, Governing Body isn't in there.