Most of these signatories have a distorted view of what is coming next with AI.
The distortion is due to their inexperience, naïveté on how difficult the next steps in AI will be, wild overestimates of their employer's lead and their ability to make fast progress, and financial incentives to hinder open source AI platforms (since almost all of them work for providers of proprietary AI systems).
As you and I know, generations after generations of AI researchers have made the same mistake: thinking that human-level AI is "just around the corner" because of some new paradigm they are working on.
They have consistently underestimated how difficult it is because they have an incentive to dismiss the limitations of their favorite paradigm as mere "engineering problems," and they can't foresee the obstacles they'll bump into before bumping onto them.
We are making progress towards human-level AI, but we're still far from it.
Some of us may have vague roadmaps for how to get there. But no one has a credible blueprint, let alone a demonstrable prototype.
Before such a prototype exists (perhaps with the learning abilities of a house cat), regulating AI R&D because of a fear of existential risk is highly premature.
There is nothing wrong with sensible legislation to regulate the *deployment* of AI application.
But legislation that hinders open research and open source AI platforms, and that makes open source AI developers liable for what people do with their code is extremely regressive.