Does the writer seem to be listening to other points of view? Would it make the reading more persuasive if they did so more or did so less?
Usually persuasive pieces are stronger if they take note of more than one point of view. In cases like this, however, the argument was made in such a way that looking at another point of view simply does not work. With the way the article was written, siding with people who were against stricter gun laws would be the same as siding with the shooter himself. The article is written by one of the students who were at school during the shooting, so the overall emotion put into this piece is genuine. This is one of the reasons why the article is so persuasive. The real argument does not come up until the fifth paragraph from the bottom. Everything that was written before it was an account of what happened on that day.
I don’t even think this article needs to look at a different perspective, this is a quite extreme case and the person experiencing it would have very strong emotions about the event.