Not saying I agree that being closed source is in the public good, although one could certainly argue that accelerating the efforts of bad actors to catch up would not be a positive.
Not really. It slows down like security over obscurity. It needs to be open that we know the real risks and we have the best information to combat it. Otherwise, someone who does the same in closed matter, has better chances to get advantage when misusing it.
Nuclear capacity is constrained, and those constraining it attempt to do so for reasons public good (energy, warfare, peace). You could argue about effectiveness, but our failure to self-annihilate seems positive testament to the strategy.
Transparency does not serve us when mitigating certain forms of danger. I'm trying to remain humble with this, but it's not clear to me what balance of benefit and danger current AI is. (Not even considering the possibility of AGI, which is beyond scope of my comment)
The US (and other nations) is not too friendly toward countries developing nukes. There are significant threats against them.
Also perspective is an interesting thing. Non-nuclear countries like Iran and (in the past) North Korea that get pushed around by western governments probably wouldn't agree that restriction is for the best. They would probably explain how nukes and the threat of destruction/MAD make people a lot more understanding, respectful, and restrained. Consider how Russia has been handled the past few years, compared to say Iraq.
(To be clear I'm not saying we should YOLO with nukes and other weapon information/technology, I'm just saying I think it's a lot more complicated an issue than it at first seems, and in the end it kind of comes down to who has the power, and who does not have the power, and the people without the power probably won't like it).