They would have never even considered killing it for any reason.... at the end of the day it was kinda his own fault, from what Ive read the set up was a camera man was directly in front of the ray, while Irwin came from behind... all whilst in shallow water. This is asking for trouble, they essentially cornered the animal... any creature would react violently in such circumstances. Unfortunately for Irwin, on land he may have moved quickly to avoid injury/death in the past, but under water you have no chance. And then of all places he was hit in the chest, any other area and he more than likely would have survived.... so lucky