This is horrible, desensitizing, and poisonous. Shame on them, and on anyone who thinks this is funny.
I don't know if I'd use words as harsh as you did, but you are most certainly on the right track. If it had been kids out in the woods hanging dead animals from a tree and playing with them, would it still have been just as “funny”?
Because my hypothetical and what happened in that school are not all that different.