My problem with this softening caveat is that the speaker acknowledges that he will present his argument in a way that will offend/sound rude/make him look like a jerk. Instead of priming my listener for thinking I'm rude/a jerk/etc. through admitting that I am, I'll just think of another way to gently criticize. Playing to one's emotions is all about being convincing, and "I don't mean to be..." is an unconvincing phrase.