> What index to start with only strongly matters when the indexes have semantics.

Which in everyday computing (as opposed to mathematics) they often do, and those cases are (most?) often, in human terms, much more natural to start from 1: "I have an array of N elements. The first of a bunch of things is thing number one, and the last of N things is thing number N." Hence:

   N_things: Array[1-N] of Thing;

   for i := 1 to N do begin

      Whatever := Whatever + Whateverize(N_things[i]);

   end; // for i := 1 to N...

Yeah, that's how old I am: That's Pascal. (With some declarations skipped, and I may have misremembered some syntax.) The canonical example is of course the original Wirth-style max-255-ASCII-characters fixed-length[1] String type: In a string of length N, the nth character is at position n in the string. Character number N is the last one.

> The one nice side-benefit of Julia's mistake in adopting 1-based indexing is that it provided an extra impetus to build machinery to handle arbitrary indexing

1) Arguably, as per the above, not a mistake.

2) Muahaha, "build machinery"? No need to build anything new; that's already existed since the early 70s. (Yeah, that's how old I am: Not adding 19 in front. There was only one "the seventies".) It's not like starting at 1 was mandatory; you could well declare

   My_fifty_things: Array[19-68] of Thing;

And then "for i := 19 to 68 do ..." whatever with it, if those specific numbers happened to be somehow essential to your code.

(At least in Turbo, but AFAICR also in original Wirth Pascal. Though probably with the max-255-ASCII-elements limitation in Wirth, and possibly also in Turbo up to v. 2 or 3 or so.)

__

[1]: Though from at least Turbo Pascal 3 (probably earlier; also think I saw it on some minicomputer implementation) with the backdoor of changing the length by directly manipulating -- surprise, surprise, it exists! String was a built-in type with its own implementation -- the length bit at index [0]. Better start out with your string declared as length 255, though, so you don't accidentally try to grow it beyond what's allocated.