The reason i've heard that some inbreeding is ok in snakes especially is because in the wild they have such a small area in which they travel. A single snake might not leave a area with a 3 mile radius (if the food and habitat are to its liking) in its entire life time. this makes its mating options minimal as compared to other animals that travel thousands of miles in a year. This is just why i heard its ok, if someone could explain why it's more acceptable in snakes then other animals better i'd like to know too.