Mrs. Elton took a great fancy to Jane Fairfax… from the very first; and she was not satisfied with expressing a natural and reasonable admiration, but without solicitation, or plea, or privilege, she must be wanting to assist and befriend her. (33)

I agree hearing the truth about themselves may hurt a person but I don’t see how the truth in this situation hurts Harriet. I don’t recall that Mr. Knightley has ever said anything to Harriet that could be construed as mean. Did I miss something? I disagree Mr. Knightley resembles Mrs. Elton’s over aggressive familiarity toward Jane Fairfax by speaking of Emma & Harriet’s friendship with Mrs. Weston (5) or to Emma of Harriet’s attributes or lack thereof re Mr. Martin’s proposal (8). He need not await solicitation or plea because unlike Mrs. Elton he has the privilege to address these topics as a first friend, a brother to Emma and as a patron and advisor to Mr. Martin.

Mr. Knightley spoke to Mrs. Weston and to Emma about Harriet but I don’t see how the truth per Mr. Knightley hurts them either for they both continue to think as they did before. Mrs. Weston continues to think the friendship of Emma & Harriet a good thing and Mr. Knightley promises her to keep his ill humor about it to himself. Emma continues to think Harriet the cat’s meow and getting rid of Mr. Martin a good thing. As far as I can tell Emma’s only lasting regret from the conversation is in disagreeing with Mr. Knightley:

Emma made no answer, and tried to look cheerfully unconcerned, but was really feeling uncomfortable and wanting him very much to be gone. She did not repent what she had done; she still thought herself a better judge of such a point of female right and refinement than he could be; but yet she had a sort of habitual respect for his judgment in general, which made her dislike having it so loudly against her; and to have him sitting just opposite to her in angry state, was very disagreeable. (8)

I did notice Mr. Knightley changed his opinion of Harriet after they danced at the ball (38) but how does that relate to the charge of meanness? I don’t think anything he said at the ball somehow casts what he said before in a mean light and he does not retract anything. This is what Mr. Knightley said to Mrs. Weston and Emma:

"But Harriet Smith… She knows nothing herself, and looks upon Emma as knowing every thing. She is a flatterer in all her ways; and so much the worse, because undesigned." (5)

She is not a sensible girl, nor a girl of any information. She has been taught nothing useful, and is too young and too simple to have acquired any thing herself. At her age she can have no experience, and with her little wit, is not very likely ever to have any that can avail her. She is pretty, and she is good tempered, and that is all. …her having that sort of disposition, which, in good hands...might be easily led aright and turn out very well.

Granted if Mr. Knightley said these things to Harriet it would be mean—but he did not say them to Harriet. This is what he told Emma at the ball after he danced with Harriet:

Harriet Smith has some first-rate qualities…An unpretending, single-minded, artless girl…I found Harriet more conversable than I expected." (38)