That example doesn't work precisely because you're conflating the concept of the loop counter (which type represents an integer that needs to be able to go <0) with the array index accessor. There's no reason for these two things to be the same type, it's just a pattern that accidentally works because we allow arrays to be accessed using a type that represents negative numbers.

What would be a more compelling argument is to use int in the same way that python does - a negative accessor means offset from the end of the array, not the start. I'm not sure golang lets you do this though...?