And to be clear, I'm just as horrified by our treatment of animals as you are but I've learned to make my peace with it. I'm just hoping that lab-grown meat becomes a viable alternative some day and we don't have to grow animals for food.
Which brings us back to the issue of the spider and the butterfly. Do you just make your peace that the butterfly will be tortured to death, or do you intervene, thus indirectly causing the spider to die a torturous death of starvation?
Another thing to consider - if we genetically engineered chickens that couldn't feel pain, would it be unethical to debeak them?
Although it is undeniable that there is a vast beauty to the living systems on Earth, that doesn't mean there couldn't be something more beautiful and alive... without so much... digestion.
Maybe humans should do better because we can, but if I am going to go about stopping other humans from committing horrible treatment, why should I then 'make peace' with how other animals behave? But to make this problem worse, look at how some animals mate. If you were to only allow peaceful instances, the species would be extinct in three generations. But maybe that is the good thing to do, because the duty is to the individual and not the species. Perhaps the humane thing to do with the spider is to not kill it, but to stop reproduction so there are no more spiders killing butterflies.
Morality sure is weird.