The biggest existential threat to us will not be from sci-fi movie like scenarios where artificially intelligent machines and robots will rebel against humans, but by the security vulnerability that this mass scale convergence could give rise to.
A less than perfectly designed system could for example impact upon the whole network and lead to disastrous consequences on an unprecedented scale. Considering that real artificial intelligence is presently at an infantile stage, it is rather silly to be tilting at wind mills when we worry about the danger it poses to humans.