I draw the line at weapons of mass destruction - nukes, bunker-busters, etc, (you know, all those things that governments create and stockpile by the megaton). Basically any item whose use entails indiscriminately kill large swaths of people within a geographic area ("killing the righteous along with the wicked", as it were) is something that represents an aggressive threat against everyone. It is illegitimate to claim such a device is "defensive" when by it's very nature it ensures immense "collateral damage" for miles and miles.
On earth, there's little to no reason for
anyone to have a nuke, for exactly that reason. But, like all bombs, it has plenty of non-weapon uses, particularly in asteroid mining. It could be potentially useful in mining here on Earth, but the fallout and such really limits the possible utility.