Perhaps it's useful to distinguish being kind from being nice in a feel good sense. Certainly we appreciate that if someone is deluded in their thinking it's a kindness to clear things up if possible, but they probably wouldn't feel too good about it at least or a time. But if kindness is only thought of in terms of being nice then that tends to favor sparing peoples feelings even if they remain in the dark, because conflict, whether internal or external isn't considered kind.
In terms of mental illness though, obviously there's an issue of stability.
