But that is precisely the sort of "dirty trick" you claim to be against. By using murder as an example, you're setting off a "boo light" (opposite of applause light) and linking it to the thing you want people to dislike. That's rhetoric, and emotional manipulation.

And it's neither a good thing nor a bad thing, in itself. Used to strengthen a valid argument, it's fine. Arguing that it's bad in and of itself is a misunderstanding... and another "boo light" (e.g. "empty rhetoric", "dirty tricks").

Emotional manipulation is unavoidable, by the way. Boring presenters and neutral presentations are just manipulating people's emotions either towards boredom and not caring, or to "respect", "status", and "seriousness", depending on the audience. It's best to deliberately choose what emotions you want to create, in whom, rather than leaving the matter to chance.