If you are, say, an unrepentant child molester serving out his latest jail sentence (this one just for owning a considerable stash of child pornography), and you're pitching a novel, it's best to leave out everything I just said in the query letter except the part about having a novel. Sure, once we get over our revulsion at your page-long, off-topic discussion of how history justifies your obsession with pre-teen boys, we'll find it amusing in an extremely dark way and laugh about it. But then we'll reject you.
I know, we shouldn't judge the author, just the novel, but there are exceptions. After all, if we took you on as a client, we would have to work with you, and if you're given to rants that make us uncomfortable, that's not a relationship we're interested in having.