If it became conclusive that Iran was on the cusp of developing a nuclear weapon, say they have a prototype ready to rest and they announced it to the world as such as they thought no one would do anything about it since they haven't so far...
Would Israel be justified to use a surprise tactical nuclear strike against Iran's nuclear reasearch sites, airforce and missile bases? The Iranians have spent a lot of time and effort re-enforcing their facilities and a nuclear option may be the most destructive and infact the only option that'd have any impact. It would be an absolute calamity if that happened for Iran, they'd lose almost all of their materials (enriched Uranium, reactors and technology), resources and scientists, cost a fortune to repair and set them back years. Plus all of the areas would be contaminated.
The way I see it, it would be Israel nukeing Iran before Iran does it to them and so we shouldn't condemn it, infact Israel would be doing the free world a favour (and Arab world) by removing this menace hanging over all of us (a theocracy that thinks a country should be wiped off the map and murders scores of its own people)