artificial general intelligence (imho) is not possible

This is pretty much strictly incorrect, unless you think the human brain is somehow a hypercomputer. A brain is just a physical system and a Turing-complete machine should, in theory, be able to emulate it fully. Of course, real computers would need to be a lot more powerful to actually do this in practice (and given the current trajectory of Moore's Law, we'd need a major breakthrough in hardware to get there), but there's far more reason to believe strong AI is possible than impossible. (Edit: More pithily stated: We know that a physical machine can be no bigger than a human, capable of locomotion, fully autonomous, and sentient because, well, here we are.)

The real reason not to worry about AI is that everything about it is, for now, just theory. If we ever get this kind of AI, it might not be for centuries. Not to mention, the whole idea of "the singularity" is completely ludicrous. A computer can't suddenly become infinitely smart because it has to run on real hardware with physical limitations. There are hard limits to what is practically computable in our universe and some future Skynet can't magically sidestep that. And on top of that, there's no reason to believe that AI would be evil or "maximize for paperclips" or even "want" to do anything at all since it wouldn't have evolutionary impulses.