In other words, there are known unknowns. There is a difference between being cautious about ID’ing because hypothetically some similar unknown species could exist (i.e. unknown unknowns), and being cautious because the taxon is not well studied in the region and it is known that many species have not been documented – we do not fully know what possibilities there are, so things like range are only of limited use as a criterion.
This is a good point. However discouraging it might be as an observer to have one’s observation pushed back to a higher level, it’s important to remember that identifiers do not derive any pleasure from doing this either. It is far more satisfying to be able to suggest an alternative, and pretty depressing to have to say over and over: this can’t be ID’d to species.
I’ve seen cases of genera where people persistently suggest a certain species because it happens to be well known (not necessarily most common) but it cannot be reliably distinguished from a couple of other widespread species without (e.g.) examination of the adult genitalia. But the species IDs may end up remaining uncorrected because IDers have discovered that they get so much ill-will from doing so that they prefer to focus their attention on other genera where their efforts feel more constructive.