The world can be a very dangerous and frightening place.
I could go on. I interpreted Witch Doctor as a fear of magic/ the supernatural. It seems silly at first but just remember all the people burned at the stake for "witchcraft" a couple of hundred years ago.
Like you said, Splitface could very likely represent a fear of mental illnesses like the one he seems to have, Dissociative Identity Disorder, a real disorder that causes people's consciousness to be fragmented into multiple identities or personalities, and stigma of mental illnesses is alive and well.
Death by radiation poisoning through a nuclear meltdown or nuclear weapons would be a pretty unpleasant way to die (obviously Meltdown) which could potentially cause terror.
Ah, the joy of starting a conversation over the psychological symbolism of a few toys. Nothing like over analysing a few plastic figures.