Truth, yes. Unfiltered, not necessarily. Most of the time, when the "unfiltered truth" comes up, the context is bad news of some sort. There are a myriad of articles on how to bring up bad news so as to keep focus on the news and not on the people.
It may well be that John or Joan is an incompetent dolt, but flat out saying so is not helpful. Dispassionate analysis of an objective failure (project delivered late, not at all or full of bugs) will make this clear, but not look like an attack on the person.
One never tells a child that he/she is stupid; what the child did was ill advised, dangerous to him/herself or others, out of line with the family's morals or ethics, but it's the act, not the person. If you can't come up with something more constructive than "stupid" when discussing someone else, you're applying the term to the wrong person,
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