With all due respect....

We often hear people insert these words at the beginning of a sentence, just before they are ready to deliver a zinger.  It begs the question, is the speaker really acknowledging respect or are these words uttered to soften the blow or just perfunctory?   My question is this: shouldn't the words that follow "with all due respect" be conveyed with respect, too?

I suspect that this phrase, like so many time-honored phrases, are merely window dressing and not delivered with sincerity.