Being too kind can also be negative, I prefer honesty and reality above the rest.
Kindness reduces barriers to accepting the honest truth and is thus part of maximizing honesty and realism.
Ie. you could also say that egoism is being kind to yourself etc.
If I feel I'm doing a disservice to the person by not speaking up, but still stay silent because I don't want to be confrontational or harsh, I don't think I'm being kind to the person. I'm only protecting the relation or myself, as I don't have the tools or a path to convey helpful information while making clear I'm having the person's good in mind.
I see it as a failure in communication (it usually can be blamed on both parties), and clearly not a character quality.