Merriam-Webster labels the word as "nonstandard" and recommends that regardless be used, all the while assuring readers that "irregardless" is indeed a word that has been in use by English speakers for "well over 200 years" and by "a large number of people across a wide geographic range and with a consistent meaning".

And, note, that same dictionary makes no disparaging remarks about the abuse of "literally" as a generic intensifier; it simply cites that usage as one of the meanings. The abuse of "literally" is more recent than "irregardless".

That tells you that "irregardless" is quite the lexical pariah. A major dictionary like Merriam is not able to wholeheartedly accept it in spite of the word's age and stability.