This is because it seems to me that the kids honestly seemed to think that John was trying to be a dick to them by having a good time when they were miserable. It's not that there's a yawning hole in their psyches where the ability to enjoy life is, it's that people are stealing an ability to feel happy that they never had, do not have and never shall have away from them. The closest they can come to real happiness is a vindictive outburst of rage against their alleged oppressors. The reason that I find this interesting is that I've not only described the choads in the balaclavas going smashy-smashy, I've also described the Foobs.
The end result is that one set of narcissistic sociopaths with a vindictive streak have to deal with the ugly antics of people just like them and they don't like it one bit.