Every online forum I have ever seen has this sort of dogpiling effect that is described. From the old compuserve BBs to Twitter. Twitter being far worse than anything around homecoming.
How much is honest opinion sharing, how much is normal human group dynamics, how much is attributable to this media? I am not sure.
But think on this one, what if someone did say something truly objectionable, and the fear of dogpiling led to no one posting any contrary responses? Only those who agreed replied. Is that better?
Should people give a poster slack? Try to make people welcome even with contrary opinions? Sure. That sounds good.
Is civility good? Cutting out peesonal attacks? Definitely.
But muzzling the community so they feel a damper on responding? Na.. JRanger to that.