When to criticize people?

You must criticize the bad. You must force people to feel shame on doing something wrong/bad. One of our main fault in the past was that we felt hesitation in talking about what is right and what is wrong, what is haram and what is halal, what is allowed and what is not. Some people may take this wrong but actually this is now the only way to stop bad, I'm not saying that kill the people who do haram things, definitely preaching should be our first weapon, but youth these days don't think or react, so our last option in this case is "criticism". You should feel shame in doing something wrong. That shame should be present in all of us.