I was 18 at the time in early May and remember it well and of course it all comes back when I hear that CSNY song. Four dead kids around my age. In the end it was the consequence of fearful, inexperienced, dishonest and immature people who found themselves in charge of a situation they couldn't handle, and they fumbled the ball. It went all the way to the top. Richard Nixon ultimately caused the Kent State massacre because the Ohio National Guard was called in because of Nixon's intolerance toward Vietnam war protests. It was pretty bad, but it would have been worse if the cause had not been gross incompetence. If knowledge of this massacre is new to you, you might want to google the Jallianwala Bagh massacre by British troops in 1919. In that case, the person in charge wanted to kill people. His men kept shooting until they ran out of ammunition.
The world is a strange and dangerous place, indeed.