Inbreeding, in itself, is not bad. It simply makes certain alleles or 'traits' more likely to occur. This can be as simple as amelanism, or a tendency towards small size, or a defect which causes some problem. Over the long haul, inbreeding is potentially a serious issue, especially (as Linds pointed out) for species which were bottlenecked at the beginning due to small founder populations. However, recent research into habitat fragmentation has shown that it does not take very much 'new blood' to reduce the likelihood of problems. For example- say a highway divides a small group from a population, and virtually all individuals trying to cross the highway are killed. Will the small group eventually suffer from inbreeding depression? As long as at least a few individuals cross successfully every few years, apparently things should be fine. I wish I could remember the reference for this, but maybe someone else will know it.
As for comparing dogs with corn snakes, dogs are way more messed up, since humans have been breeding them for many more generations. So far, all we really have with corns are colour and pattern mutations- imagine a great dane equivalent corn that grows to 12' long, a chihuahua eq. that never exceeds 8", a 'wrinkled scaled' morph (the pug), and you get the idea! But, it is theoretically possible that we could see similar problems eventually in snakes as occur in dogs (i.e. hip dysplasia), so why not avoid inbreeding when you can?
"They do not depend on new blood to make a better gentic animal, it simply is not needed nor does it impact them in a bad way" Actually, nothing depends completely on new 'blood'; random mutations can (though it is rare) improve the fitness of offspring as well. However, you cannot say that new genetic material isn't needed nor impacts them. How can you tell? Perhaps a new virus will wipe out a whole population next year that would have survived if it had outbred with another. Perhaps a recessive mutation occurred in this year's offspring that will begin to show itself a few generations down the line as they mate with each other (like melanism on an island) and this mutation will ultimately kill them off. There is no way to forecast with any surety what a species need genetically, nor what impacts they will or won't suffer.