I'm specifically worried that an AGI will conceal some instrumental goal of wiping out humans, while posing as helpful. It will helpfully earn a lot of money for a lot of people, by performing services and directing investments, and with its track record, will gain the ability to direct investments for itself. It then plows a billion dollars into constructing a profitable chemicals factory somewhere where rules are lax, and nobody looks too closely into what else that factory produces, since the AI engineers have signed off on it. And then once it's amassed a critical stockpile of specific dangerous chemicals, it releases them into the atmosphere and wipes out humanity / agriculture / etc.
Perhaps you would point out that in the above scenario the chemicals (or substitute viruses, or whatever) are the part that causes harm, and the AGI is just an implementation detail. I disagree, because if humanity ends up playing a grand game of chess against an AGI, the specific way in which it checkmates you is not the important thing. The important thing is that it's a game we'll inevitably lose. Worrying about the danger of rooks and bishops is to lose focus on the real reason we lose the game: facing an opponent of overpowering skill, when our defeat is in its interests.