I would like to say two things about that.
First, I mentioned the Polytechnique massacre, but I could have mentioned the incident at the University of Waterloo, when someone stabbed a gender theory professor for those same reasons. I and my fellow trainers at the organization wondered whether we too were in danger when giving our training sessions. Would I be stabbed next for talking about gender theory? I'm being sarcastic with the use of air quotes.
Second, I think it's very interesting to note that the concept of dangerous speech came about when statements made prior to acts of violence such as genocide and war were studied. Why do humans act on something or agree with certain types of violence?
When you instill fear in someone by telling them that people in the LGBTQ+ community are coming for their children, you are using an argument that is going to cause a lot of violence. If a parent feels that their child's safety is at risk, resorting to violence will seem much more acceptable to them. This type of threat mobilizes a lot of people, but it can also be a caricature. We've seen trans women caricatured a lot in relation to their use of women's bathrooms; they are depicted as sexual predators. That rhetoric becomes dangerous because it gives people permission to defend themselves against the threat.