The question is probably too broad to be useful. I see several situations where it is extremely healthy to a society and several situations where it can be harmful and even countries like the United States restrict it.

My freedom of speech (under US law) doesn't allow me to go around accusing my neighbor of pedophilia, for example, without opening me up to a hefty lawsuit if they are not, in fact, a pedophile.

Even in this forum we're using right now (founded by an organization associated with a man who once wrote an essay titled "What You Can't Say"), there are things I could transmit here which would result in a swift, merciless, and I argue just ban from our benevolent moderators.