These sorts of thought-experiments ask me to imagine that I am in an epistemic (and practical) position that I cannot ever really occupy.
They ask you that because they are designed to point to particular issues with moral reasoning, so they are about that one issue and nothing else. It may help to think of it as not “if you were in this position” but rather as “if an ideal reasoner, who uses your moral system, were in this position”.
The issues still exist in situations that are not so clear cut, but in those situations it’s easy to pretend that they never come up at all just because they’re not front and center.
They ask you that because they are designed to point to particular issues with moral reasoning, so they are about that one issue and nothing else. It may help to think of it as not “if you were in this position” but rather as “if an ideal reasoner, who uses your moral system, were in this position”.
The issues still exist in situations that are not so clear cut, but in those situations it’s easy to pretend that they never come up at all just because they’re not front and center.