"We could still achieve the same effect if we started indexing at 1, but it would require more code, and it would be less clear."

Really?

How about dealing with strings?

"123456789" how many chars we have? 9

char[1] = 1

char[2] = 2

:

char[9] = 9

Now, let's try the C approach:

"123456789"

char[0] = 1

char[1] = 2

:

char[8] = 9

where is char "1"? at zero index!

how many elements we have?

last index plus one!

see? there is already confusion in place, or as you say, more code and less clear...

"0123456789"

  ch[0] = 0;
  ch[1] = 1;
  ch[2] = 2;
  :
  ch[9] = 9;

  ch[1] = 0;
  ch[2] = 1;
  ch[3] = 2;

....

Please re-read his question: "how many chars we have?" "how many elements we have?"

  ch[1] = 0;
  ch[2] = 1;
  ch[3] = 2;
  ...
  ch[10] = 9;

This is about having the Nth element of the array with the index N rather than N-1.

That's not code, that's English.

When we start indexing from 0, the only time we need to do a +/- 1 is when we need to index the last element. All other times (iterating, mapping) we don't need to.

Also, starting indices at 1 would change the idiomatic iteration to:

   for (int i = 1; i <= SIZE; ++i)

I find that the <= and >= operators add more to my cognitive load than the strict relation operators < and > because there's an or in there. I don't find the alternative to that idiom any better:

  for (int i = 1; i < SIZE + 1; ++i)

Your original argument was that we should make it easy for humans to understand, not computers. I think that starting indices from 0 is easier for humans to understand because it simplifies the code we must write and read.

No way I would trust a language design with your semantics for this syntactic construct: for(i=1;i==n;i++)