It's fractal. It's like beetles in the evolutionary tree, millions of species, but in relation to the wider tree they're all just one branch of the insects.
I like the analogy, RG, but when one looks at the JWs and Mormons, you realise that they are closer to Islam in the way that they regard Jesus as a human and a prophet than to Christianity.
Trinitarianism has managed to propagate the view that it's the one true Christianity, ...
whereas I would argue that non-Trinitarian ideas have tried to jump on the 'Christian' bandwagon, rather than Trinitarianism propogating the 'view that it's the one true Christianity'. I accept that it wasn't until the 3rd century or so that the Trinitarian principle was finally tied down, but when one looks at the New Testament, even the oldest documents have it as a core concept, without which the life, death and resurrection of Jesus actually has no meaning. Furthermore, the idea of a single God being multi-faceted goes back to the Old Testament
... but a more rational system would use the word Christianity to cover all faiths centred on the NT.
In fact that would be one of the most irrational ideas out. There are so many sects and groupings who use the name 'Jesus/Christ' as a sort of hook, but without using any of the rest of the NT, as to make that a non-starter. You might as well continue to call Buddhism a sect of Hindism!!
There's less difference between the lot of them than there was between flavours of 1st-century Judaism.
I'd disagree; the difference between, say, Mormonism and mainstream Christianity is probably greater than between Islam and Christianity.
The answer to the question Why aren't we all Jews? is that we all are, it's just that the word Jew has become much more specialised than it used to be.
Sorry, but the word Jew has very specific meanings, both ethnically and religiously.
If Tiberius or Tacitus came back today, they'd think we were all Jews. Even the neo-pagans would think like Jews to an ancient Roman mind. Their thinking was stranger than we can imagine.
I very much doubt it. After all, even they realised the difference between the Jews and the early Church