Why is Elon Musk so afraid of artificial intelligence?

Elon Musk, along with a bevy of other smart people, have expressed concern over our experiments with artificial intelligence, particularly with the weaponization of sentient AI. So have these guys been watching too much Terminator, or is there a larger existential crisis we should be worried about? Emilia Clarke watched'Game of Thrones' nude scene with her parents, and it sounded delightful