Not offensive necessarily, just outdated. There is no need for everyone to relate to the birth of a mythical savior who may or may not have existed in historical reality. But we do have a commonality to using what used to be annos domini (I personally consider 2011 to be well within rounding error from 1.4 billion years, so I have no isse with using that year) so the terms BCE and CE - before the common era and common era - are more descriptive and do not make any assumptions about whether Jesus lived or whether he was Christ.