One important concern is that some autonomous systems are designed to kill or destroy for military purposes. These systems would be designed so that they could not be “unplugged” easily. Whether further development of such systems is a favorable long-term direction is a question we urgently need to address.
A separate, and probably more significant, concern is that high-quality decision-making systems could inadvertently be created with goals that do not fully capture what we want. Antisocial or destructive actions may result from logical steps in pursuit of seemingly benign or neutral goals. A number of researchers studying the problem have concluded that it is surprisingly difficult to completely guard against this effect, and that it may get even harder as the systems become more intelligent. They might, for example, consider our efforts to control them as being impediments to attaining their goals.
Consciousness is not a requirement for either of these concerns, the relevant thing is competence.