"Inbreeding brings it all out, outcrossing does not. Outcrossing gives you multiple "hidden genes", some good, some very bad. Eventually those hidden genes are going to come out, but you don't know when, or in what way, or how many animals will be or are affected. Inbreeding is like opening the closet door and letting those skeletons out. You inbreeding, and it brings them out, now you can see them, now you know what you have, now you know where it came from, and you can take some action to eliminate it."