Trump: 'a whole civilisation will die tonight'

Once the First Use Taboo is broached, nuclear explosives will be used for everything. Wherever you have a spare 100kg of payload and a hardened or area target - nuclear explosives, from a weapon effect perspective, are simply too good not to use, once the cat's out of the bag. It'll be like machine guns in the early days of WW1 - where they broke the taboo of using them on _civilized peoples_ - but in this metaphor each bullet being the most powerful device made by Man.

Breaking First Use - particularly against a non-existential[1] threats - might rank among the worst single decisions in human history.

[1] or non-existent

Morality starts with definition, and there are other ways to deal with these things than courts. For instance, boycotts.