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Bullying and hazing are contagious. Most of the people like that experienced some degree of it before, either by being born in the "correct" conditions and watching others being bullied/hazed, or more likely by being bullied/hazed.
Ultimately, the contagion spreads upon the promise of getting a little rush of power from dishing out abuse on the next person targeted and reinforcing the infected with a sense of stability and security in the established norms.
To my infinite shame, I used to be like this. I was bullied a lot, and I internalized that to mean I was an inferior and unworthy person. The flipside of that was that, on the rare occasions I could be one of the bullies, I jumped at the chance because (in my mind) it proved that I wasn't entirely without value.
The fact that you acknowledge that, feel regret for it, and I can only assume you have sought atonement for it means a whole lot.
I've known childhood bullies that never changed and in fact looked back at the "good old days" where "boys could be boys." 
Gotta reify your relationship to hegemony. What if you were slightly weird? You'd at least want people to know that at least you were loyal to the idea of "normal".
Also some people relish in participating in hierarchy (as long as they're punching down). >.>
wrote a bunch on this. Gotta discipline the body and otherize to justify oppressive power systems.
ideology. it's extremely powerful and will compel people to essentially become cops enforcing social norms often going as far as using actual violence or killing. neurotypical, patriarchal, cisheterosexual norms. we live in a society etc.
People that say ideology/social conditions miss the point. While bullying is certainly shaped by these factors, it is just normal human behavior that needs correction.
It exists in all children, regardless of location or culture. It has to do with maintaining social hierarchy and forming groups. Children making friends and children excluding others are just two sides of the same coin of primate social structure. Some people grow out of that but most don't, they just learn to hide it better. In fact, most bullies go on to live far more successful and fulfilling lives than most people.
Human beings are not inherently good or bad, they are inherently very smart pack animals. At our best, we can come together with millions of different people to complete amazing political/social projects. At our worst we have racism, bullying, and genocide.
it is just normal human behavior that needs correction
Yes, but where does that human behavior come from? Material conditions.
Believe it or not, there are some things that humans just do because they're not complete blank slates. It's like avoiding pain, or having a natural inclination to love parents and family.
The only way your point is true if include genetics as a "material condition" but that doesn't conflict with what I said.
It exists in all children, regardless of location or culture.
Tho I think your issue is conflating teasing with bullying (the latter is more systematic, long term and doesn't tend to arise outside of totalising institutions like school, work, bourgeois family, etc).
Ahistoricism is not good theory. When you study cultures outside of state formations and burgher societies you find a much wider variety of behaviour, and a greater degree of acceptance of 'weirdness', both on an economic level (e.g. various anishinaabe families and even individuals having idiosyncratic ways of harvesting maple sugar, saying "do it properyl" isnt socially acceptable), an aesthetic one (see the vast varieties of clothing that natives chose to wear in the earlier phases of colonialism 1600-1800, for example), or personal or spiritual choices (e.g. some of the prophets of the Nuer in Sudan ate excrement or ashes, some spent hours arranging seashells into neat patterns). You'll also see variation in cosmologies, and people accepting random teenagers just saying "all the elders stories are wrong, I know how the world was actually created" with little more than an eyeroll. One of the best examples of the acceptence of difference (and why even outside of just being a decent person its important) is the Shawnee prophet Tenskwatawa (younger brother and main theorist and agitator behind Tecumseh's war). He was basically useless most of his life. He maimed himself early in life failing to shoot a bow properly. He spent the better part of a decade doing the Shawnee equivilant of couch-surfing and bumming food off everyone else while aquiring a drinking problem. He was still socially accepted, if not trusted with any particularly important tasks. Then, one day, he drank a fuck ton and had a vision and turned into an anti-colonial prophet/propagandist. In our society, people would go "lol drunk failure go away". In his society, people listened and he helped mobilise one of the biggest anticolonial wars against the US.