Interesting perspective, thanks. Yes, I think the term Judeo-Christianity is often used for purposes of alliance or assimilation. (So the idea might just be rhetorical or imaginary.) Sometimes Jews will use it for Christians' benefit in a "we're just like you" kind of way, setting up for "we want your support for X cause..." I'm currently reading K. Healan Gaston's book on the history of this term. I suppose some people might use the term to refer to the Hebrew scriptures that are shared by both religions (i.e. "Old" Testament), or to interfaith families, but if they meant those things then they'd just say that.