It’s clear that regardless means, ‘without a regard’ while irregardless, when broken up, is a double negative. So it’s understandable why this word would irritate those who appreciate the subtleties of the English language. Many people put up posts against Merriam-Webster’s choice.
They posted their website explaining their decision, saying, “The reason we, and these dictionaries above, define irregardless is very simple: it meets our criteria for inclusion. This word has been used by a large number of people (millions) for a long time (over two hundred years) with a specific and identifiable meaning (“regardless”). The fact that it is unnecessary, as there is already a word in English with the same meaning (regardless) is not terribly important; it is not a dictionary’s job to assess whether a word is necessary before defining it. The fact that the word is generally viewed as nonstandard, or as illustrative of poor education, is likewise not important; dictionaries define the breadth of the language and not simply the elegant parts at the top.”
They categorised the word as an adverb and specified it’s a nonstandard word meaning regardless. They even included a FAQ section explaining the word was first used in 1795, it has been included in other dictionaries and that are other similar words.
As our world grows and changes, languages evolve too. So dictionaries are always growing. Their main goal is to clarify the meaning of words in use and their decision to define irregardless will make it easier for those looking up the word to understand it and it’s history.