would you kill a stray that attacked your pet?

A friend from work lives on a lake. Some time ago he found a wood-duck hatchling that was separated from its mother and proceeded to bottle feed it by hand and raise it in his yard. He built a chicken wire pen for it to stay in.

One day, he goes outside to find a stray dog inside the pen with the juvenile duck (couldnt fly yet) in its mouth. According to him it looked like a cross between a dog and a coyote. He busts in there and the dog drops the duck, which runs off into the water and swims away in the lake (for the first time i might add). So he takes the stray, which is not aggressive and is mainly looking scared according to him, and throws it into the lake. It can't swim and starts to drown, and he feels bad about it, so he gets a long net and drags the dog back to shore, and lets it go.

My first thought was that I would have killed that mfing dog with a machete. I thought about it, and now I'm not sure if I could have, if it was not aggressive towards me. The dog was just being a dog. WWTOBD?