Studies would show that a thousand other things are also followed by an increase in violence. In literature, movies, telephone calls – anywhere people communicate with other people, you will find that some people communicate offensive (to someone) ideas, and as a result, other people who are prone to violence will be pushed over the edge and do something harmful. Those who seek violent ideas will find them regardless of censorship. And those who seek positivity and love will find them.
It is absolutely "just speech". We haven't crossed any magical boundary today that we hadn't crossed 229 years ago when the bill of rights was ratified. If you want to fully prevent violence from ever occurring by censoring speech, you're welcome to live in a communist country. But of course, you won't find what you're looking for there either.