Okay, I know this. It has to be "The fact that Northern opinions of slavery can be hypocritical"
The author wanted to have people see themselves in Miss Ophelia so that they could reconsider their views on slavery.
I hope this helps some! :)
Answer:
Mainly because of the Anonimity that comes with cyberbullying. You do not know who is on the other side which gives them protection from law enforcement and so on