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.
If OpenAI can do it, I would not say that that is very unlikely for someone else to do the same. Open or not. The best chance is still that we prepare with the best available information.
But if we hide the things, we have no idea what we are trying to control.