Arbitrary indexing is fine as long as people are sane about how they do things and don't assume. In almost every language these days you can use this or something analogous:

  for x in some_collection

Which is great if you don't need the index, and if you do need the index then you want the equivalent of:

  for i in some_collection.range

or

  for i, x in some_collection.enumerated

Being forced to use 0-based or 1-based or even strictly integer-based indexing is the wrong thing. If you want to use characters/runes as your index you should be able to. If you want to use some enumerated type, you should be able to. And if you want some subrange of one of those, you should be able to.