An absolute tragedy. But I do not know what else the zoo staff could have done. Harambe was a 30 stone beautiful wild animal. Whilst we can sit behind our keyboards and pontificate, we cannot get away from the fact that no one knows what might have happened. He was a wild animal, and no one, but no one can say how he might have reacted (since I doubt very much that he has ever had a four year old he does not recognise fall into his territory).
Whether the zoo security was to blame, or whether the parents were to blame are all questions for another day to attempt to ensure it does not happen again. I have no doubt it was not a decision taken lightly by the zoo who get to know the animals and care for them.
Necessary but unnecessary is the best way I can describe it.