There is a saying about imperfection of any individual vs the perfection of gathering of them; everyone knows everything.
So you may not know that one of your actions is not good, or there exists a good thing -that you do not know- to follow. Even sometimes, in spite of knowing what is good and what is bad, you may forget it and you may need someone to remind you to go on the right path. So, the need for being invited to a good action, or for a reminder to prevent you from a bad doing is now clarified.
Now, in a society where everyone supposes it a responsibility to supervise other people, it is less likely to see crimes. On the other hand, it is more likely to see a wave of morality.
In true Islam, there is a to-be-obeyed instruction in which you are responsible not only for your own deeds but also other people. In this rule, you are obliged to invite people to good deeds, such as being truthful, helping the poor, having trust in God, and so on. Besides, you have to prevent people from doing bad actions, let it be saying bad words or causing harm to someone.
Yet, this rule is to be done under some specific conditions, such as causing no harm or bad effect to you or the society, hoping for any effect on the person that is being invited to sth or prevented from sth, and, of course, your true knowing of what is bad and what is good!
So, if we want a moral world, full of peace and justice, we'd better invite one another to be a good person, and also, before it is too late, we'd better let one another know about the wrong deeds and try to prevent it.
Now, can you describe a case for us in which you can practice this teaching?
PS-I wanted to choose another topic containing "true Islam", but due to the wave of Islamophobia that exists in the world, I changed it to the current topic.