Sure but you could just nuke us too, given that the response to a mass civilian death event would be the same. Same reason the US would be foolish to destroy the Three Gorges Dam.
It doesn't need to be a mass civilian death event. They can wait, collect data and kill 90% of our most important soldiers, heads of state, spies and everyone needed to maintain critical sectors of our economy. They could kill everyone who is anti-china. They could kill all the members of one political party (any one) as a false flag and cause a civil war.
Surveillance technology is nessisarially selective, so these "all or nothing" hypotheticals do not apply.
