"The teacher went back to where the two were sitting and literally slammed her hand down on the desk and said, "How do I know you are not saying something bad?"
As a former high school teacher, I get it. There are days when you just are on edge. I once through a persistent problem child out of class because she sneezed. I just didn't have the fight in me that day.
I am hoping, based on the quote, that this teacher was having one of those days. Too bad for her it has become a meme on Facebook. There might be a context to this story beyond the article.
This reminds me that ethics is something to which we work because, put simply, we need less of this in the world. The default reaction to what we don't know is often fear, but that is something we can work to overcome.