It isn't a matter of harm, but rather a proper inclusion. While there are differences between Judaism and Christianity (and their respective sects), we are all pretty much agreed upon the matter of ethical behavior - And I might hasten to add that the 'Old Covenant' was just as instrumental in setting up our country (laws and precedence) as the New Covenant... Before there was precedence here, and well after into the 1960's and '70's The Bible was considered suitable for that task. There is no other holy book that shares that level of secular respect. And therefore, credit where credit is due: The 'Old Covenant' is wholly creditable to Israel and no other (at least on this mortal coil), even if Christianity supposes the 'New Covenant' is not (which I disagree with, btw).
Hence the "Judeo-Christian" appellation.
Why do you ask? Does it offend you?
It should offend all Christians, since it implies that "Christian" is insufficient and that only areas of alleged overlap with "Judeo-" matter.