You're right, that seems like a much better question, or at least a more potentially useful one when it comes to identifying bad characterization. And yet... how many books can you think of where the hero or heroine is widely disliked by people who are not, in some way, the "bad guys"?
Of course, "bad" in this case doesn't have to mean "given to committing villainous acts" -- it might just mean that they are ignorant, or bigoted, or jealous, or self-absorbed. But the characters who dislike Our Hero aren't presented to us sympathetically in the way that the hero and his friends are. We aren't invited to consider their judgment as sound, or to identify with them in the same way. And I really can't think of an exception to this rule at the moment.
Of course, you might write a book in which the heroine is evil and we are meant to anticipate her downfall. In that case, the heroine's enemies would be the "good guys". But even at that, you're still left with a situation in which the attitude of the other characters to the heroine is a touchstone of their moral worth. It's just that in this case, their moral worth is proven by their *opposition* of the heroine rather than by their support of her.
So, perhaps even that question isn't as useful in identifying Mary Sues (in the sense of unrealistically idealized or intrusive, reality-warping OC's) as it might seem...
Re:
Of course, "bad" in this case doesn't have to mean "given to committing villainous acts" -- it might just mean that they are ignorant, or bigoted, or jealous, or self-absorbed. But the characters who dislike Our Hero aren't presented to us sympathetically in the way that the hero and his friends are. We aren't invited to consider their judgment as sound, or to identify with them in the same way. And I really can't think of an exception to this rule at the moment.
Of course, you might write a book in which the heroine is evil and we are meant to anticipate her downfall. In that case, the heroine's enemies would be the "good guys". But even at that, you're still left with a situation in which the attitude of the other characters to the heroine is a touchstone of their moral worth. It's just that in this case, their moral worth is proven by their *opposition* of the heroine rather than by their support of her.
So, perhaps even that question isn't as useful in identifying Mary Sues (in the sense of unrealistically idealized or intrusive, reality-warping OC's) as it might seem...