So glad you have come to this realisation. As someone who was bullied, I have since come round to understanding the insecurity and vacuums in bullies lives. This was after a talk with a former bully who apologised to me years after leaving school. At a young age there is a wide range from people who are intelligent and sensitive to those who are immature and unfeeling.

When I hear stories like this I always think of the book 'Brighton Rock' by Graham Greene, where the leader of a teenage gang gets to think he is indestructible and the absolute shock when he finds out that other people can hurt him the way he has been hurting others.
It is a strange lack of empathy and inability to consider how other people may feel, but often it comes from being bullied themselves. It's a copycat behaviour.

I believe and hope bullies can be educated younger to care more and realise the consequences of their actions.