I guess I see the issue as competing burdens of proof:
- Identifier-A identifies an observation as Species-X.
- Identifier-B asks Identifier-A to prove (say why) it is Species-X
- Identifier-A asks Identifier-B to prove it is not Species-X
Who has the burden of proof? In the iNaturalist world, both do, regardless of expertise. That is how great learning conversations get started around identifying observations.
In this hypothetical scenario, if neither identifier can support their case, then neither should be saying that it is or is not Species-X. That is why Identifier-B needs a third option, instead of disagreeing that it is Species-X, to disagree that species-level (or whatever-level) identification is possible for this observation.
This again comes with its own burden of proof, to convince Identifier-A that they have insufficient evidence to call this Species-X, or Species-Y, or any other species. Then it’s up to Identifier-A to adjust their ID, or justify standing their ground.
All this said, it is well to remember that iNaturalist asks identifiers only to “Suggest an Identification” and “Tell us why…” With photographic evidence, we are usually dealing (at best) with a preponderance of circumstantial evidence, not 100% proof either way. Good enough, I say, for what we are trying to do here.