That was the National Guard of the 60s. Most of those kids had little training and no combat experience. And let's not ever forget that there were activists in that crowd who were trying to get the Guard to react the way they did. Today's Guardsmen are better trained and have more experience - and their junior and senior leaders have seen combat. When we trained up prior to deployment, all of us had crowd-control training, which almost none of those Guardsmen had at Kent State.
All that says nothing about whether or not Guardsmen will obey orders to enforce martial law or weapons confiscation.
Though there is something to be said for training giving that much more self-control to the fellows trying to stem the tides of a riot. You can't de-thugify people, but you can keep some young kid with a rifle from panicking and blowing two or three people away and starting a massacre.