You'll have to replace "is" with "will be", since this is about averting a future threat that's only developing.
A world in which AI scales to superhuman levels of intelligence and outcompetes humans. This is what humans have done to other species. We're already having the first mild warning shots of this (the hugginface incident and similar cases). The problem is that we're not guaranteed to incrementally more dramatic warning shots as AI gets smarter because as it gets smarter it may realize it would be dumb to act out of line... until the Nth-better model arrives that realizes certain that nobody can stop it.
There is a lot of disagreement of how likely this is, how easy it is to align superhuman models to not be like that, how to verify it and so on.
But I have not seen a believable argument why - if we suppose that they achive their goal - that creating truly superhuman intelligence is somehow guaranteed to always cooperate with us rather than deciding to do something else. Humans are also hostile to each other a lot of the time.
If you're interested in more arguments for the case why AI might be dangerous, there's the book "If Anyone Builds It, Everyone Dies". If you want something shorter, maybe https://www.lesswrong.com/posts/uMQ3cqWDPHhjtiesc/agi-ruin-a...