I just don't like it
It is about me. I should be the one spreading the news to my friends. How would you feel if your friends come to you and prode more about the news when you are wondering how in the first place he heard the new from? How would you feel if you are not ready to tell everyone the news yet and all of a sudden, everyone knows about it already?
If you need to spread the news on my behalf, the least you can do is ask me if it is alright or not first. Sometimes, there are things that are too early to announce.