Pointlessly killing animals/or abusing for pleasure can, in fact, can be a very troubling behavior and be a sign of something being very wrong in a young child. However, animals are not humans. A child killing animals for pleasure does not automatically mean serial killer or human abuser. It is something that requires close monitoring, and possibly professional help.
(http://www.psychologytoday.com/blog/...als-when-worry)
An adult killing animals for pleasure is not one step away from becoming a serial killer. Heck, I'll admit that I enjoy hunting, but I would never hunt an animal for the sole purpose of killing. (there will always be another factor, usually food or population control)
It disturbs me to hear of a family teaching young children to kill pointlessly. Animals may not be humans, but they're certainly worthy of our respect. You will catch more flies with honey, though. It's easy to go on the instant defensive of something we love and are passionate about. But you must understand that most people view venomous snakes as monsters who are out to get their family. They think they're teaching a valuable lesson.
Instead of instantly involving our emotions, we want to calmly educate people, and bring honor to our hobby, you know?
Not everyone will listen even after that. But that's okay. It's also the time to walk away. (And unfriend their butts!!)