If only more people...
believed in Evolution this could quickly be explained & dismissed.
Young species, eager to prove their prowess & superiority over another rival species will look for ways to show their greater abilities (due to adaption) by tormenting or killing the potential rival. And thus one species survives and the other becomes extinct.
It is the true beauty of survival of the fittest.
The boys should be given an "A" in their science classes.
Please remember that values are a mere human construct and the outrage you feel has been the result of socialization, not due to instinct or neurons in the brain or especially some silly mythology called religion. Other cultures would praise and give higher status to these ambitious hunters...thus, please do not pass "judgement" on them and realize that this is a recreated ritual hunting that has been eliminated from western culture in the past 1000 years.
at the core of every behavior is a philosophy people...think about it.