Friends why cruel?

In the media, we know that a friend runs a knife in another friend's chest, the friend pelted from the roof and chased another friend or a group, beaten him to death, and killed a teenager. Sometimes the dog is slaughtered and near the friend! The headline of the news is, the guardians scold, the sensitive reader's two eyes wiggle but the procession of death does not stop.
Where is the problem? Why can not friends be friends, what is so angry anger or jealousy that turns a man into a monster at once. Why are friends so cruel? What does our children read in school-college, make them violent? Can not family education make them tolerant, or are the technology and the media responsible for their intolerance? It is not right to think that the matter is only limited to our country, this intolerance around the world is limited, this intolerance around the world. Those who have studied the human mind and society, tried to find out the reasons for this cruelty, atrocity.