Bullies are almost always extremely powerful both physically and socially,

Very often it's just one or the other, and not necessarily "extremely powerful" either. There are lots of people who are looked down upon by most of the people in their life and use whatever little bit of power they have to abuse people with even less power to feel better about themselves.

and know society will always take their side.

The state often will, but broader society is in fact different from high school.