I've seen some positive changes in how my husband behaves toward me since his MLC. In fact, he points these out to me when he feels I am upset with him. He truly believes he is being a better person in some regards at least. Maybe it is compensation for the bad, and maybe he is an exception, but I think it is unfair to say they turn all bad and turn their back on morals altogether. It might be more fair to say they pick and choose what suits their image and their needs.
Even if you believe in demonic possession, normally a possessed person does not act possessed all the time. The demon comes and goes. In fact, that is how it becomes so obvious, because it is like they become another person sometimes and then return to themselves.