Read this article and then this editorial.
Knee jerk luddites are going to be quick to blame the Internet and the unregulated social networking sites like Facebook. Me, I see the fact that this happened on Facebook a plus. Why? Because the disgusting creeps got caught at it.
In the olden days before the Internet, local thugs would just stalk and harass a person like this. Given their alienation from society, the victim would be unlikely to complain and would continue to put up with it. Either the thugs either get tired of their game, or they wind up beating the homeless person and leave them in a ditch somewhere. Actually, this still happens today.
Because these creeps advertised what they were going to do, they got noticed, and they got caught. Before something really unfortunate happened. Facebook helped society this time.