Well I suppose you can assassinate nuclear scientists, bomb the shit out of the facilities, and withhold development aid and necessary technology regardless of whether you have nuclear technology. Once bombs are on the table, boundaries are out the window.
I can't tell to what extent you're being sarcastic. Your final sentence seems to have suffered during editing, but I gather you hold it as absolute that no unstable regime should have access to nuclear power, and that it is impossible to determine the difference between the risk of an unstable regime and a stable regime holding nuclear power, from which I infer that you hold it absolute that stable regimes should also not have access to nuclear power.
Are you seriously saying that someone wanting nuclear power is legitimate grounds for war? If you were the leader of some country that would have about a 50% chance of success, would you declare war on Australia, now that they've announced they intend to pursue (limited, though surely particularly risky) nuclear power?
I don't know if you know the relevant history, but I am specifically referring to the precedent of Israel bombing the Iraqi reactor. Gaddafi also had a nuclear program that would have gotten him in trouble if he hadn't stopped it in time.
I don't want to categorically endorse nuclear weapon programs (or even civilian programs) as a reason to go to war, but I can understand why some countries believe so. Particularly in the case of Israel, when countries like Iraq and Iran have specifically and repeatedly said they want to destroy Israel. The nuclear programs in the hands of Iran, Pakistan and China are already troublesome. Their current governments might seem relatively "rational" about the whole thing, but they are authoritarian and who knows what will happen with their next crop of unelected leadership.
In less egregious cases, highly radioactive material is sufficient to build dirty bombs. A simple regime change, civil war or whatever in an unstable region with nuclear power could lead to a nightmare. Even less sinister, simple incompetence can lead to a mismanaged reactor or waste disposal, which in turn can have wideranging and catastrophic consequences.
I can't tell to what extent you're being sarcastic. Your final sentence seems to have suffered during editing, but I gather you hold it as absolute that no unstable regime should have access to nuclear power, and that it is impossible to determine the difference between the risk of an unstable regime and a stable regime holding nuclear power, from which I infer that you hold it absolute that stable regimes should also not have access to nuclear power. Are you seriously saying that someone wanting nuclear power is legitimate grounds for war? If you were the leader of some country that would have about a 50% chance of success, would you declare war on Australia, now that they've announced they intend to pursue (limited, though surely particularly risky) nuclear power?