When I was a boy (long time ago) a cat killed all my seven pigeons in one night but took none of them. I began to write slogans everywhere saying "Exterminate felinity." And "Death to cats."
That is an unfortunate tale. I am reminded of the "Frog and the Scorpion" Fable. The behaviour of some creatures, or of some people, is irrepressible, no matter how they are treated and no matter what the consequences.
I don't know 'The frog and the scorpion' fable, but I know that most cats are vicious killers, especially the ones which visit my garden and kill fledgling blue tits born in my nest boxes.
I know what you mean. Last year I rescued a fledgling Blackbird that had fallen from the nest in my gutter. I kept it safe each day in my son's trampoline enclosure and the parents would fly down and feed it. It did flying practice and managed to get a few inches higher each time. All the while, it was being watched by my neighbours crafty cat. One day it was gone. The zip to the trampoline had been opened and I went out of the gate to see the cat slinking away with the bird in it's mouth. I hated that cat for a while too.