Honestly it just seems natural from my point of view. Ajin in the end are not human and the psychologist was completely rational when he explained that once ajin are discovered they will feel the psychological difference between being able to die and struggling for survival and not being able to die. I mean the old guy was just evil but for the masses I think it is completely justified to mark the ajin as dangerous considering the messed up experiences ajin go through.
Good point, this stuff is natural but sometimes I really feel like it wouldn't be. But then again there are so many other cases and that have other options and at the end it gets too comlicated
thing is, along history, mankind has done the same things they're doing to Ajin to fellow human beings. it's not the fact that they feel threatened, but the fact that they CAN do such things to them -at the beginning if you remember those guys trying to catch Kei (Kai? hey where's his friend BTW?!), they weren't feeling threatened, they just wanted to catch him and sell him... just saying
....I don't know what to do with mankind anymore. Personally I'm disappointed that mankind would do such things.....