I've found a sort of pattern in people's reluctance to believe that AGI poses an existential risk. If you think of specific scenarios about how AIs could take over the world or kill everyone, people will say, "oh, that's easy to avoid, we can just do X". If you think of scenarios that are hard to avoid, like an AGI designing and releasing a deadly, virulent virus (or lots of different ones), people will say, "but why would AGI want to kill everyone?" If you point out how AGI might have very good reasons to get rid of humans, and that we don't have any way of really guaranteeing they won't try, people will say, "but we won't give them any power". If you point out that once we make AGI, it's inevitable that somebody somewhere will give it power, and even if they don't, it's very easy for someone very intelligent and sociopathic to manipulate gullible people, they say something like, "well, we superintelligence probably isn't even possible", or "we can't even agree on what intelligence means".

Turn it around for a second. What does it take for humanity to have a good future after we create intelligences smarter than us? Let's say the AGI listens to and obeys humans. Well, one thing we need to avoid is just an absolute chaos of terrorism and war. It's easier to do damage than to prevent it, and if everyone has an obedient, mastermind scientific genius in their back pocket, you could have it invent a pathogen and cure in tandem, keep the cure secret and release the pathogen, and do this over and over until your enemies are all dead.

So we need AGI that is aligned with humanity, in the sense that it won't do stuff that hurts people even if someone tells it to. How do we do that, and not potentially end up with AGIs that can't be corrected if they get some idea that turns out to be wrong? Ideally, we'd make AGIs that have a bias toward inaction, that are "lazy" in a sense, and try to do the minimum they can. But those AGIs won't be as useful as ones that work like eager beavers toward some goal, so there will be selection pressure towards those.

I think the way to look at it is like with evolutionary biology. The pressure that evolution puts on animals to develop certain genes/behaviors is similar to the pressure that humans will put on AI development, and it ends with AI being more capable and more likely to follow orders even if those orders mean bad things for other people. As they get more and more powerful, this means chaos. It's monkeys throwing poo, vs monkeys throwing rocks, vs monkeys with guns, vs monkeys with rocket launchers.

And look -- I'm not certain that things will end in disaster. But inventing something smarter than you and trying to stop it from taking over sooner or later seems very difficult, and I can't even get a good answer out of people who think it'll be fine, or good. The default case is not that it'll be fine, the default case is we have no idea how it'll go. It's a grey fog. Just because humanity has muddled along and managed not to destroy ourselves so far, does not mean that we're safe, by any means.