Important distinction: children get their genes from us and share many of our values by default. Computers do not share many of our values by default. Instead they do what they are programmed to do.
But the problem is that computers do what you say, not what you mean. If I write a function called be_nice_to_people(), the fact that I gave my function that name does nothing to affect the implementation. Instead my computers behavior will depend on the specific details of the implementation. And since being nice to people is a behavior that's extremely hard to precisely specify, by default creating an AI that's smart enough to replace humans is likely to result in a bad outcome.
