Why talk about things if you don't know anything about it

I do not understand why people talk about things that they do not know anything about. A friend of my family was killed in a car accident a few days ago, and there are so many stories going around about what happened. If you do not know what happen, then do not say anything at all. Another thing, if you do not have anything nice to say about it, then please do not say anything at all. Friends and family members read what you say. How would you feel if someone was saying that about one of your friends or family memebers. SO PLEASE WATCH WHAT YOU SAY.