Because if it isn't, you
probably shouldn't be saying it.
And if someone says it to you, you should definitely not repeat it. Dare I say, even tell them that it was unkind, unnecessary or untrue? Because you should.
You never know the damage you can do, the lives and relationships you can destroy by saying things that are unkind, unnecessary and untrue.
And generally, what you say about others says far more about YOU than it does about them. Trying to taint the good name of others, whether you happen to like them or not, never will bring the satisfaction or adequacy you are seeking in your own life.
Just a thought.