It’s tricky, isn’t it. I believe wholeheartedly that as things currently stand, the onus on the observer should be to declare what the subject is, and the onus on the identifier should be to respect the observer’s intent—and to ask for clarification if necessary.
However:
It is difficult when an observer makes observations in which the subject is uncertain. The best an identifier can do in the current set up is to ask for clarification, but it relies on the observer taking action in response. If the observer isn’t on iNaturalist very often, or is new, or is not particularly diligent, these requests for clarification may go unfulfilled.
Now all that is rightly frustrating, and is particularly so when the observer is a repeat offender, so to speak. But it is how the system is set up. A solution, of course, would be to say that an observer does not have a right to declare the subject of their own observation—but I think that would cause more problems than it solves. Another solution would be to allow curators to split up or duplicate observations with more than one potential subject—this could be a gentle helping hand for new or inexperienced observers, and would prevent irritated non-curators from making rash modifications.