A student or a non-student shit stirrer at Kent State fired the first shot. It was intended to provoke a violent incident.
What should have been the rules of engagement for the National Guard? Wait until someone takes a bullet before firing?
I've never heard or read that, though I don't doubt it. But this makes my point: Even if the soldiers have no intention of firing on Americans, they are likely to be placed in a scenario where their options are very limited. And as you point out, the Rules of Engagement will be vague, but defined by the Generals who owe fealty to 0bama.