Children who are physically abused often become physically abusive themselves, engaging in fist fights at school or outside the school environment. They may, then, become abusive in their interpersonal relationships, as well. This is a behavior that indeed threatens society!
It socializes children that this is the only way in which human relationships can function, particularly those between family members--father and child, husband and wife, siblings--and so there is a tendency to replicate those relationships in the abused child's adult life, perpetuating a vicious cycle.
I agree with Pohnpei. When children are stuck in abusive situations, they see no way out--no future without abuse. Unfortunately, while they may be able to eventual escape the abusive home, the pattern is usually repeated in their future lives. This affects their spouses/partners and children. And it affects their spouses/partners and children. And so on, and so on. Breaking the cycle of abuse is VERY difficult.
To me, the biggest effect of child abuse is that it makes the abused child much more likely to be an abuser in the future or to be the victim in an abusive relationship. This is terrible because it means that the abuse that happens at an early age continues to impact the child later in life.
I would suggest checking out a link like this one for more information about various aspects of this problem.
Here's my firsthand opinion.
It's damaging to self-esteem. We feel unloved, and worthless. We get the sense that everyone is out to get us, and develop an instinct to get them before they get us. I developed a quick, sharp, silver tongue. Children who are abused may also be scared to be close to anyone.
A bit grim but I need the info for a discursive essay!