How can a soul not be immortal? This is one of those dogmatic principles promoted by Christians that makes absolutely no sense, but which is constantly spouted off much to their detriment. I guess it probably makes sense if you're a meat-eater and you don't want to think about the fact that the poor creatures being slaughtered have a consciousness like yourself, but from a theological perspective it is just total hogwash. This is definitely a case of demonic influence using its power over man's intelligence to justify lusty desires.

Behind the concept is the materialist idea that animals aren't living creatures, but instead something more like a biological robot controlled by chemical reactions.

So do people who suffer from MR/DD not have immortal souls?

An animal eats, sleeps, mates, and defends. Don't you do these things? Obviously, humans can do something animals cannot-worship God through spiritual practice. Many humans do not have spiritual practices though, so does that make them animals?