I think that position would be a lot more defensible if they weren't giving another for-profit company access to it. And there is definitely a conflict of interest when not revealing the source gives them a competitive advantage in selling their product. There's also the question of if the source is too dangerous to make public, how can they be sure the final product is safe? An argument could be made it isn't safe.
It is safer to operate an AI in a centralized service, because if you discover dangerous capabilities you can turn it off or mitigate them.
If you open-weight the model, if dangerous capabilities are later discovered there is no way to put the genie back in the bottle; the weights are out there, anyone can use them.
This of course applies to both mundane harms (eg generating deepfake porn of famous people) or existential risks (eg power-seeking behavior).
I don’t think this belief was widespread at all at that time.
Indeed, it’s not widespread even now, lots of folks round here are still confused by “open weight sounds like open source and we like open source”, and Elon is still charging towards fully open models.
(In general I think if you are more worried about a baby machine god owned and aligned by Meta than complete annihilation from unaligned ASI then you’ll prefer open weights no matter the theoretical risk.)
