Has it ever occurred to you the Iranians might be interested in such a weapon because Israel already has one?
This is not without precedent. We know for example that Pakistan developed its nukes to deter India when they demonstrated they have nuclear weapons.
> it plausibly deters Iran from advancing (and thus using) its nuclear weapons program
As for Iranian intentions; they’ve been quite clear and consistent that they want to wipe out Israel, and I take them at their word about their motives. It seems unrealistic to me that they want nukes for purely defensive purposes (unrelated to their broader desire to wipe Israel off the map), i.e., they think (absent a nuclear Iran) Israel would without provocation initiate a nuclear attack on Iran. It seems obvious to me that Iran wants nuclear weapons as part of its broader desire to eradicate Israel, albeit probably not to launch nukes at Israel directly but rather to derisk a nuclear counterattack. In either case, a nuclear Iran brings us considerably closer to a violent humanitarian crisis.