Responses
While I get what you're saying, the guy was a victim in the first place (not that it erases what he did, of course) and they were his parents. In time of despair most human will find something to blame, it's unfair but it's natural, so I don't think their reaction is repulsive.
I find it repulsive that the parents of the dead guy blamed Kanoo for shooting their son (in a flashback in chapter 5) when their son murdered the entire hospital staff on a rampage and who knows how many more people he was gonna kill if he wasn't shot.