I've searched through lots of the code I've written, and as it turns out, I haven't found one case where being having 0 as a "negative" index would have helped. :-p So while I still like it better my way, I don't have a real use case to show.
From another standpoint, maybe it's just that I don't want to rely on the behavior of something like (cut '(1 2 3 4) 3 1), where the indices are reversed. If I can exempt (cut '(1 2 3 4) -3 0) from that error/undefined zone (in a way that's smoothly consistent with cut's other behavior), then cut may be slightly more useful to me at some point. But yeah, I don't know exactly when it would pay off or whether some other behavior would be better.
