I like the point MouseKilla brought up about it all goes down to whether you think a cat or dogs life is worth more than say a mealworm, mouse, rat, etc. I personally value all life the same. I've had many pet mice, so it's kind of sad to even feed MICE to my snakes. But all in all, the snake needs to eat. If the cat or dog is going to be euthanised anyways, they don't really have that animals life in high regards anyways, so why not make it useful. Carnivorous animals need to eat, and as the owner of such an animal, I guess it's up to you where to draw the line, whether you think mice and rats are lower beings or less alive is completely up to you. To me, all life is the same but I also respect that the animal needs to eat.
In conclusion...Here kitty kitty kitty
"A rattlesnake that doesn't bite teaches you nothing."