This is how society/culture works. Seriously bad actions will/should be disapproved of by others. It's how you regulate things.

(There does need to be a way to navigate the information and false claims (court, etc) because the majority don't always have all of the details and we don't want ideological mobs to make off the cuff choices to kill people).

In the case of Charlie's death, we as a society have chosen, based on logical thinking and experience. that murder isn't a good idea. So we don't need to prove it was bad, it is.

Back in the day, if you did something bad to your group/village they ostracised you and you were on your own. This is fairly normal stuff.