I assume you did not find the etymology of the word “irregardless.” According to Merriam-Webster, “irregardless” is a blend of the words “irrespective” and “regardless,” and not “regardless” formed by adding the prefix “ir-.” I understand your point, but clearly that “irregardless” has passed the criteria set by lexicographers for it to become a word itself, unlike the other ones that are product of confusion and mispronunciation. Here is the link to the video I am talking about. Perhaps this should help you understand.
http://www. youtube. com/watch?v=5_fUMcTb1jI