Rhetorically speaking, "I don't want to sound rude" can have the opposite effect as the one intended by the writer (when I'm on the receiving end that's almost 100% of the time). It basically states, from the get-go, that the opposing argument is so deeply flawed, requiring such a strong, ruthless counter-argument, that there's a good possibility that you might offend your interlocutor's sensibilities. Even if you're so fucking right that your answer erupts from the depths of your logical mind with the power of a thousand volcanoes, that's not a good way to create rapport. At this point, no one knows your reasoning yet. You may sound like a douche bag. You may be right, but not as right as you think. You may also be very wrong, and in that case you not only promised something you couldn't deliver, but you also made it hard to take the conversation forward. Because, by belittling your interlocutor, you created an environment where getting it wrong is not admissible, and he/she will apply the same rule to yourself. Even in the case that you're right, your behavior discouraged further questions. All because you wanted to be nice! Communication is hard.