As long as the computers which form the "brain" don't have security systems that they control, then we can always pull the plug.
Of course we'd have to be prepared for manual control of services which were previously taken care of by computers, which would lead to a lot of economic difficulties, most certainly a worldwide economic depression, but it's that, or become slaves to computers (worst case scenario)
As long as we place limits on the system, and "teach" it proper moral values, then we'll be fine
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Common Sense isn't all that common