I completely agree with you as far as criminal trial and punishment is concerned. However society has parallel and independent responsibilities to the state. We don't deal out punishment for crimes. We are a much higher authority. We fund law enforcement and our representatives make the law. We determine the society we wish to live in.
We have a very important role debating how our society should work, electing people to represent our interests, educating our young, and setting acceptable standards of behaviour in our community. Calling people out for bad behaviour is our civic duty. Political opposition, investigative journalism, human rights groups, environmental groups and anti-fascist groups all help keep us informed of dangers and abuses.
We have a very lop-sided defamation environment where the rich and powerful intimidate critics into silence. I think we have enough silence. It is right to be cautious about vigilantism. There is a reasonable middle ground between us having our heads in the sand and pitchforks.