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.
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.