It sounds like you might not agree with that belief.
While I don't agree with their actions here, I do think there's sufficient reason to hold that belief.
On some fronts (e.g. security, on which you've experienced more than me), I think there are surmountable challenges. But on other fronts (e.g. bio), a single errant actor could reasonably kill millions or billions of people with sufficiently powerful AI. We don't have good defenses here, and those actors do exist.
I still don't agree with these actions, but I do think I agree with their assumptions.
The model release cards for Opus have repeatedly and consistently stressed that the model doesn't have the fiddly know-how that's required to provide meaningful assistance in possibly dangerous subfields of biology. Mythos (Fable without the overly strict guardrails) has shown improvements in things like drug design, but even then the situation isn't really that different. This risk is ridiculously overblown, and the way to manage it sensibly is to introduce meaningful oversight for actors that seek to order the actual specialized materials involved (especially any synthetically generated genes/proteins/whatever).