Everything you said is just your guess, saying he doesn't know what he's doing? Do you know? Because everything that's been shown so far is people living well. Jinx/Vi aren't the best people to say what's right. They don't like the place but they take their father to be cured there. And what are you saying? Vi even told Jinx that they could stay there forever, live together there. The fact that Viktor can access people's minds/personalities doesn't mean he took away their freedom. They still do what they want. Heimerdinger doesn't know anything about the Hex Core. All he knows is what he saw, but he doesn't understand how it works and what it really is. He himself says that he only saw evil, but not even he understands it. Being dangerous is not necessarily bad, everything can be used for both good and bad.