From what I have read on some internet sites the reported ill effects on those being the target of on-line bullying is exactly the effect they hope and strive to achieve.
If they desire to affect the mental health and well being of those who are the target in this way, it begs question as to the state their own mental health and well being in allowing their participation in such aberrant behaviour.
A single troll is bad and bad enough if you are its plaything of choice ... organised gangs are in my opinion something entirely different and portray distinct deviant behaviour.
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Depression and anxiety are common mental health challenges among people who have been cyber bullied. Loss of self-esteem and confidence are also commonly reported.
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People need to understand not to jump on the on-line bully bandwagon by joining in a conversation to have fun at someone else's expense.
Irrespective of why someone chooses to be a Troll, the destructive consequences of their behaviour make it inexcusable.
http://www.womensagenda.com.au/career-agenda/lessons-learned/trolls-the-damage-they-do-and-what-you-can-do-about-it#.VQ3uG_msU7s