Can you consider that for instance, in @ishiki's case, an entire school's company has issues like this? Including teachers, janitors, parents of the students, etc.? This means that only a select group of people worldwide initially has at least a neutral perspection of this world, meaning they are of good nature and mean no harm whatsoever, until they get bullied, and that the rest of them (the attacking group, consider this almost the entire world population when we go by your reasoning, ) are bullies and people of low worth by nature? It must mean that the greatest percentage of this world's population is purely evil and closeminded (the latter I won't argue about, however, as this is entirely true). Usually it has nothing to do with the bully's self-esteem or self-worth. These are likely perfectly fine, as people like this usually have tons of good friends and solid relationships, and the bullying solely exists because these people will have themselves to praise once they prove they can control someone.
People always seek differences from themselves and feel an insisting need and pressure to point other people on these differences. This cannot be done subtly, subtleness in pointing someone on their "mistakes" simply does not exist. The victim will always feel attacked, will always feel undermined no matter what strength someone persists they bear within themselves. The reaction that is caused is what triggers bullies to continue; they have an effect on someone — and negatively affecting someone is much easier than positively affecting someone. Especially during highschool, it's a challenge to succumb to emotional situations that involve positivity or even a neutral state of mind regarding a certain issue, or person. It is much easier to bear a grudge against someone, to point out what is unlikeable about their clothes, their hair, their manner of speech, or their interests, especially if these are particularly different from what the usual trench of teenagers prefers. You must wear brand clothing, you must enjoy the modern day music (pop, hip hop and r&b only, anything that hasn't appeared in the charts is an abomination), you must be willing to gossip and talk badly of other people, you must drink, smoke, have lots of unprotected sex, and possibly even enjoy other narcotics, and partying until you'll either end up passed out in someone's bathroom or even in the hospital is required at least once or twice in a lifetime. I have learnt that anything that strays from this behaviour is not accepted — or at least you'll end up with fewer friends and acquaintances because you would not fit into the widely accepted flock of sheep because you'll have nothing in common with those people.
Today's generation is especially bad, surely bullying has existed throughout mankind's entire existence but it hasn't come to the surface as strongly as it has in the past two decades. Bullies cannot be taught otherwise. Selfishness is in our nature and it will never leave our system. The only thing we can do about it is improve our mental healthcare as something to crash upon after an extended period has passed, as bully-awareness does nothing to schools or work-environments. It cannot be stopped, it cannot be solved by any organization or a grand speech by great speakers. Bullying is, and will always remain a taboo, no matter how much the issue is pressed upon from time to time,