Psychologists suggest that to cure cruelty

It's pointed out in the passage that

1. 
   aggressiveness is the result of parents using authoritative approaches against the child
   
2. 
   the aggressive instinct of a person can only be cured by psychologists
   
3. 
   parents aren’t aware of dangers of repressing the aggressive instinct in the child
   
4. 
   in serious cases of cruelty, parents' or teachers' understanding approach won't be a sufficient cure
   

Most headset stereos have one thing in common: they can cause hearing loss. Studies have shown that sound levels from the machines can reach 115 decibels or more - roughly equivalent to standing 100 feet from a commercial jet at the moment of take-off. At that level, permanent hearing damage can occur after just 15 minutes. And the earlier a child begins using a headset, the more damage can accumulate. Loud noise causes hearing loss by killing irreplaceable hair cells in the inner ear. Normally, the process occurs slowly as people age, but noise damage can accelerate it. Noise-induced hearing loss is insidious; damage may not be apparent until later in life. Since headsets are used privately, parents often don't realize how loud their children's music is.