Uhm... although they're over-reacting, it's not as hillarious and joking as you people seem to think it is.
It's basically a death threat, or a wish of death. It's basically stating "i wish x person was dead" in that sense, and it is supposed to be taken seriously in that sense.
Books like that have been confiscated and a problem for decades, things like this went on in the 50's. People would write in books about who they hated, and who they wish would die.
The majority of the time, these were written by unbalanced kids, and they had different psychotic tendencies(please understand the defenition of psychotic if you're going to reply about it). Even in that interview, his "friend" pretty much says that he is these things. Is it something that should be taken literally, as if he is trying to kill them? No, but it does show that he's an unbalanced kid that thinks he would be happier if people died, and that is a serious issue.
But you guys laugh at it, sure it's kinda funny that they're over-reacting, but it is still a serious matter.