Terminology of Christianities and Judaisms

Is it just me or is there something rather annoying about the trend over the last twenty years or so to talk about early Christianity as "Christianities" and early Judaism as "Judaisms"? I must admit that I am hoping that this is going to prove to be just a fad and something that we will look back on in twenty years time as an odd terminological aberration that characterized a particular kind of scholarship at the turn of the millennium.

I understand, of course, the anxiety people feel about attempting to convey just how varied Judaism and Christianity were in this period, and it is natural to want to stretch language norms when one is examining emerging Judaism and Christian origins. But I can't help feeling that there is nothing helpful, interesting or insightful about this particular terminological oddity. If the variety of Christianity is not properly understood as "Christianity", then I don't see how calling it "a" Christianity in any way advances the discussion. It is either a variety of Christianity that might legitimately be described as a variety of Christianity, or it is not. Calling it "a" Christianity simply doesn't change anything. Likewise Judaism.

And is it not the case that Christianity is far more diverse today than it was in the first two centuries? Many Christians within particular traditions do not recognise those in other competing traditions as Christians; there are Christian sects that are not called Christian by their founders; there are Christian sects that are not called Christian by their critics. We have every possible variety of belief and practice within contemporary global Christianity yet we don't feel the need to use the term Christianities. And likewise Judaism. Why, then, do we feel it necessary for the early centuries?