The point is, you're unlikely to have a system that starts out with the goal of making paperclips and ends with the goal of killing all humans. You're going to have to deliberately program the AI with a variety of undesirable values in order for it to arrive in a state where it is suited for killing all humans. You're going to have to deliberately train it to lie, to be greedy, to hide things from us, to look for ways to amass power without attracting attention. These are all hard problems and they require not just intelligence but that the system has very strong values - values that most people would consider evil.
If, on the other hand, you're training the AI to have empathy, to tell the truth, to try and help when possible, to avoid misleading you, it's going to be hard to accidentally train it to do the opposite.