As much as you may want to blame Destiny / Bungie, this type of behaviour has nothing to do with either. This is a symptom of the internet. As WhiskeyJohnnyO pointed out in his post, people think that they can say / do whatever they want without consequence because the internet provides them anonymity.
Yes those dudes were a bunch o’ dicks for verbally abusing a kid, yes they were in the wrong, but he could have left the party at any point and then blocked and/or reported them. It shouldn’t have come to this point, but children must be educated about the internet and how to respond to situations like this.
He didn’t deserve it, but hopefully he will have learned from it and will be able to handle similar situations in the future.