Well, the way that I came to terms with this is by reminding myself of the following:

If you keep the feeders comfortable and well fed before offering them, they're getting a better quality of life than they would in the wild for the short time they live... They don't really get to know suffering.

In the wild the same thing would happen - it's the natural order and who are we to violate it. The snake needs it for survival... We don't often feel bad when we eat a steak or a hamburger, but that's because we don't need to see the animal being killed. Feeding our snakes is a humbling experience, it forces us to recognize the brutality of nature, but it's just that - nature.

Another thing that seems to help is not playing with the feeders and naming them... That's going to be my issue for sure!