Animals do those ~bad things~... dolphins rape, etc.
The term 'rape' doesn't really come into it, that would count as a simple attempted reproduction. Animals killing animals is simply the natural order of things, higher primates killing other primates (baboons etc.) could be seen as a stronger parallel but even then it is simply the course of nature, even when they seemingly do it for 'pleasure' they are still acting on their base instincts and animalistic behaviour. You could turn the argument around and say that we as humans, no matter how intelligent we like to think we are, are still driven by our base animalism and an attack like this is a 'natural' human adolescent act.
However I don't believe that. We do have a higher level of intelligence and we should act and behave accordingly, and according to the rules and taboos of the society we have built with that intelligence. Burning a dog alive is truly disgusting and I would say 'evil'.
I really hope they get caught.