Kent State is a classic case of historical revision. The majority of Americans supported the National Guard’s actions, in part because they were in valid fear for their lives after the rioters started throwing bricks at their heads.
Revisionism you say? Most accounts say that before the National Guard was involved, most of what was thrown was beer bottles at police cars.
The Wikipedia article on the shootings doesn't mention the word "brick" once. It also says:
"While on the practice field, the guardsmen generally faced the parking lot, about 100 yards (91 m) away. At one point, the guardsmen formed a loose huddle and appeared to be talking to one another. They had cleared the protesters from the Commons area, and many students had left.
Some students who had retreated beyond the practice field fence obtained rocks and possibly other objects with which they again began pelting the guardsmen. The number of rock throwers is unknown, with estimates of 10–50 throwers. According to an FBI assessment, rock-throwing peaked at this point. Tear gas was again fired at crowds at multiple locations."
So there were rocks being thrown at National Guard members who were ALREADY teargassing the boxed in group AND had knelt and aimed weapons.
Somehow you extrapolate that to average people going about their day and randomly taking a brick to the head... huh.
So even by your account, the rioting students were attacking the guardsmen by pelting them with rocks, and the guardsmen opened fire to defend themselves from this attack. That's a clear instance of justifiable force.
