Until the admonition "Love thy neighbor as thyself." becomes the global norm, humanity will continue to be plagued by violence in all its ugly forms.
We know this already. Story after story in books and movies relate it. Love conquering evil/hate. Is there any more common theme? Well, yes, I guess there is. "Good" beating "Bad" through the use of violence. "American Western" stories and movies. They are a lie. When, in real life, have we seen the Bad stop after the Good guys "win". Stories have an end. Life doesn't.
Love thy neighbor as thyself. No more "us and them", just us. It is the only answer.
It isn't just about war and crime, though. Even indifference is a form of violence. How can we have billionaires and people living on the street? Us and them.
Refugees from wars and genocide. Us and them.
Economic and racial prejudice that creates slums and gangs. Us and them.
As my blog title implies, disequilibrium of power is at the heart of most of society's ills. (Overpopulation is at the heart of all of humanity's ills, but that's another topic.)
Nothing creates violence faster than making someone helpless. You want to get at the core of why mass murderers act out? Look at helplessness and hopelessness. Why do people become radicalized? Because they feel helpless in the face of powers that are antithetical to their values.
Power. The thirst for it. The lack of it. The disparity of it. All the things that provide it: land, resources, money, beauty. Power is at the core.
The struggle between social bonds (love) and competition for the resources needed to survive have, undoubtedly, been with us since the earliest days of humanity. Nay, since our primate ancestors became social creatures and overpopulated their territory. Somehow being in small groups and competing for food must have been more successful than working as one large group.
So, we come by it rightly. But, we are, supposedly, intelligent beings. We should be able to see the damage caused by our thirst for power, right? We don't. In aggregate, we haven't evolved, emotionally, from our ancestors. As we overpopulate Earth and individually struggle to survive, in toto we're the most destructive creatures to ever inhabit the planet. And, we create enormous suffering in the process.
Our most beloved teachers, Buddha, Muhammad, Christ, Gandhi (and others), taught about the dark side of power and greed. They put forward the solution in various forms of the Golden Rule.
"The Golden Rule or ethic of reciprocity is a moral maxim or principle of altruism found in nearly every human culture and religion, suggesting it is related to fundamental human nature." (Wikipedia, https://en.wikipedia.org/wiki/Golden_Rule)
Muhammad and Islam:From the hadith, the collected oral and written accounts of Muhammad and his teachings during his lifetime:
A Bedouin came to the prophet, grabbed the stirrup of his camel and said: O the messenger of God! Teach me something to go to heaven with it. Prophet said: "As you would have people do to you, do to them; and what you dislike to be done to you, don't do to them. Now let the stirrup go! [This maxim is enough for you; go and act in accordance with it!]"Ali ibn Abi Talib (4th Caliph in Sunni Islam, and first Imam in Shia Islam) says:
— Kitab al-Kafi, vol. 2, p. 146
"O' my child, make yourself the measure (for dealings) between you and others. Thus, you should desire for others what you desire for yourself and hate for others what you hate for yourself. Do not oppress as you do not like to be oppressed. Do good to others as you would like good to be done to you. Regard bad for yourself whatever you regard bad for others. Accept that (treatment) from others which you would like others to accept from you... Do not say to others what you do not like to be said to you."
— Nahjul Balaghah, Letter 31 
You shall not take vengeance or bear a grudge against your kinsfolk. Love your neighbor as yourself: I am the LORD.
Gandhi:“An eye for an eye will only make the whole world blind.”
― Mahatma Gandhi
"I object to violence because when it appears to do good, the good is only temporary; the evil it does is permanent."
"Power is of two kinds. One is obtained by the fear of punishment and the other by acts of love. Power based on love is a thousand times more effective and permanent then the one derived from fear of punishment."
"What difference does it make to the dead, the orphans, and the homeless, whether the mad destruction is wrought under the name of totalitarianism or the holy name of liberty or democracy?"
"There is a sufficiency in the world for man's need but not for man's greed."
Buddhism:560 BC, From the Udanavarga 5:18- Hurt not others with that which pains yourself.
If you want others to be happy, practice compassion.
If you want to be happy, practice compassion
The Dalai Lama
Christianity:"Do to others what you want them to do to you. This is the meaning of the law of Moses and the teaching of the prophets" (Matthew 7:12 NCV, see also Luke 6:31)
"A new commandment I give unto you, That ye love one another; As I have loved you, that ye also love one another. By this shall all men know that ye are my disciples, if ye have love one to another." John 13:34
Love, compassion, sharing...these are the only antidotes for the greed and violence that are destroying us.