All Kyle had to do to not have any of that happen is not show up. The odds of that dramatically increased when he decided to show up with a gun where he knew a bunch of people, some of whom would would be armed, would be out in force and opposing his views.
Much like a lone women wandering late at night through a crime-ridden part of town getting raped, he may not have done anything wrong, but his bad judgement led to the expected consequences. And before we talk about defending his workplace, there's a reason many places say to not try to stop robberies - the insurance claim is far cheaper than the cost of most outcomes of trying to stop the thefts, even the relatively positive outcomes.