The above-mentioned researchers are skeptical in different ways. Andrew Ng thinks that human-level AI is ridiculously far away, and that trying to predict the future more than 5 years out is useless. Yann LeCun and Yoshua Bengio believe that advanced AI is far from imminent, but approve of people thinking about long-term AI safety.
Okay, but surely it’s still important to think now about the eventual consequences of AI. - Absolutely. We ought to be talking about these things.
+1 To go even further, I would add that it's unproductive to think of these researchers as being on anyone's "side". These are smart, nuanced people and rounding their comments down to a specific agenda is a recipe for misunderstanding.
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Yoshua Bengio, one the world's leading expert on machine learning, and neural networks in particular, explains his view on these issues in an interview. Relevant quotes:
I think it's fair to say that Bengio has joined the ranks of AI researchers like his colleagues Andrew Ng and Yann LeCun who publicly express skepticism towards imminent human-extinction-level AI.