Because the adversary is important to the question.

Americans, what level of Chinese provocation would warrant a US nuclear strike? How about Russian?

Anglo-French, at what level of Russian provocation would you support your country independently using its nuclear capabilities?

Russians, American/Chinese provocation

Chinese, Russian/American provocation

Indians/Pakistanis, each other and for Indians, China.

Israelis, Arab world.

I have deliberately not provided casualty estimates, as A. I just had this idea for a topic, B. That's a lot of research, C. I want to see how your opinions change once I give cold hard numbers. But, I suspect you will all look it up anyway to avoid looking disproportionately hawkish/dovish. D. Because there are different attack options.