I can't imagine a valid ethical justification for not releasing the model training details which they withheld. I'd speculate that they did it only to slow their competitors, but I don't have to because "the competitive landscape" was the reason given right there in their paper.

There is (IMHO) no good reason to let OpenAI argue simultaneously for "this technology is too dangerous to be replicated" and for "... but if you have a credit card then you can use it right now".