Tell Your Children: Words Have Meaning
I think the issue may be that either parents or schools are not helping kids to understand that certain words are incendiary and considered hate speech. (Maybe schools need to have assemblies with skits to explain this or perhaps Ballard's great film/video program could produce some videos.)
Many students know about the First Amendment and may believe they can say whatever they want to whoever they want. There are countless court cases to prove that belief to be incorrect. One of the easiest ways to explain it this concept, even to younger students, is to talk about not being able to cry, "Fire!" in a crowded theater. Speech that can incite is open to legal action.
One story is the situation at Western Washington University from a couple of weeks ago that started around a discussion about whether their mascot, a Viking, is representative enough for their population. As things do happen on social media, a lot of racially-charged statements - mostly anonymous - went out.
There had been a claim that during this back-and-forth, the student body president, who is African-American, had called some white students "baby KKK." That led to one student saying online at Yik Yak, "Let's lynch her." He removed that statement very quickly but many people saw it including the student body president who was rightly frightened. Screenshots were Seattle Schools Community Forum: Tell Your Children: Words Have Meaning: