O.K. I don't believe you about the gangs of children beating people with stones..has it happened ? probably so...there are billions of people on the planet..but it is EXTREMELY rare...so let's just agree to disagree...
Now Lions? no way ..A pride will kick out young males when they begin to get a mane and eat too much and sexually mature...the prides male/s handle that almost always...the ousted young males will team up and scavenge until they are mature and attempt a takeover of another pride...You made that up about the lions....now female lions will on kick out a female member if times are tight and food os scarce but when the prey is plentiful they are welcome to rejoin the pride...hippos ? male hippos will kill challengers yes..but they do not live in any sort of bonded society..the alpha male gets the best water hole and all the bitches that want to eat and lounge there...and breeding rights...monkeys? an ousted alpha is killed or demoted to bottom wrung ....Nature has it's own way to prevent incest and young males are often driven off when they begin to take interest in mom or sisters.....