> Why would you need to learn to deal with bullies?

Because bullying is an extreme example of a common human power dynamic.

> If you try that the modern world as an adult you get charged with aggravated assault, pick up a criminal record and then are weeded out from polite society

Fair enough. I was thinking exclusively of non-violent bullying. (It may get physical. But in a roughhousing way. Not one intended to cause pain or injury.)