We Humans tend to try to make our pets and their life styles fit into our pre-conceived notion of what they are as animals, and how they should be cared for. You have just crossed over the line into broader understanding. Welcome!
As a Reptile enthusiast with decades of experience with many species of snakes, and at least 4 species of Kingsnakes, I'd like to share some profound facts:
1. Many kingsnakes prefer reptiles over rodents. In the wild this is especially common in more desert areas where reptiles are more common than rodents. One biologist found that 80% of the diet of Mojave Kingsnakes consists of rattlesnakes. Mine love lizards, especially Fence Lizards and Skinks.
You will find that your snakes, like Humans, are INDIVIDUALS. Their food prefernces, even color of prey, may vary from specimen to specimen. Give them what they prefer! Fence Lizards are common in the wild, and are even abundant in many locations. So are anoles in the SE part of America.
2. Most wild animals have some parasites. Situation normal, as they normally pass thru the body during defecation. Normally, only a buildup of waste presents a parasite problem. Adult parasites are destroyed during digestion, only the eggs & larvae are the problem, but they normally pass thru in the normal cycle. Avoid buildup of waste in the enclosure and you generally avoid parasite problems.
I've fed wild-caught lizards of several species to both my Cal King and Baja King. Neither has ever had mite nor parasite problems.
3. Live prey is best for your animals. It's less convenient for Humans; best for snakes. Like you, they NEED live food & enzymes for proper metabolic processes to occur. No wild snake eats frozen-thawed animals, and they only rarely scavenge. They are ambush hunters which eat live prey.
Oh! You've heard horror stories about uneaten prey killing the snake! Okay, contact the person who wrote or told you that and get from them the:
A. Date? Location? Contact person? Ooops! Another nasty rumor quickly dispelled once you press for evidence. This has only rarely occurred; I've never known it to occur and I've kept snakes for decades…
4. I don't have snake pets; I have animal companions housed in natural biomes. Mine have extra large enclosures which mimic their natural surroundings - including rocks, lichens and native rocks & plants if possible. They enjoy interacting with me, too, especially the Garter snakes (which tend to be more inquisitive than Kings.)
The more we give them what the need to thrive, as opposed to a cage or sweater box with one hiding spot, the better they perform. That way, we are no longer domesticating wild animals; we are extending & recovering their natural range.