Why numbering should start at one

Where are the use cases? Some algorithms are expressed more easily origin-1, others in origin-0. If you must choose one and want to do it rationally, you need a set of use cases ranked by relative importance.

The origin choice may be easy to change in the language syntax, but once you have users, it's not so easy. User programs make assumptions about origin. So does the code generation phase of the compiler. In most cases, the assumptions are implicit and not explicit; after the fact changes are difficult.