They say AI will destroy humanity because they believe it. OpenAI and Anthropic were created by people who believed this. There's nothing nefarious about them saying this.

Why are they still building it? Because each team thinks that THEY are the ones who can prevent it from destroying humanity, but they have to get to AGI first, before the other teams make an AI that does destroy humanity.

But also, if AGI doesn't destroy humanity, it would be the most powerful weapon in the world, and they want to be the ones in control of it. Keeping the focus on Armageddon distracts from the real and severe problems that arise if a single person, or even a small group, controls an AGI.