For those who do not want to use the Twitter link, here is a cut-and-paste version of its content.
The core thing to know is that Irregardless isn’t some sort of freakish monstrosity, standing hideously apart from all the other beautiful, perfectly formed words of English. All it is is morphologically irregular, which means that it’s not a strict combination of its parts.
There are *plenty* of morphologically irregular words in English. For example, there are approximately 200 verbs with irregular past tense forms. Yet no one is up in arms that we say 𝘀𝗮𝗻𝗴, 𝘄𝗿𝗼𝘁𝗲, and 𝘄𝗮𝘀 instead of 𝘀𝗶𝗻𝗴+𝗲𝗱, 𝘄𝗿𝗶𝘁𝗲+𝗲𝗱, and 𝗯𝗲+𝗲𝗱.
While those words are all missing a suffix (the regular past tense -𝗲𝗱), irregularity pops up even in words that contain the expected suffixes. Consider: 𝗿𝗮𝗯𝗯𝗶𝗻𝗶𝗰. The root is clearly 𝗿𝗮𝗯𝗯𝗶 & the suffix is -𝗶𝗰, which forms adjectives. What is the 𝗡 doing there?
Other similar words are: 𝗽𝗿𝗼𝗯𝗹𝗲𝗺+𝗶𝗰 → problem𝗔𝗧ic 𝗵𝗮𝗯𝗶𝘁+𝗮𝗹 → habit𝗨al 𝗵𝗼𝗿𝗶𝘇𝗼𝗻+𝗮𝗹 → horizon𝗧al 𝗽𝗲𝗿𝘀𝗼𝗻𝗶𝗳𝘆+𝗮𝘁𝗶𝗼𝗻 → personifi𝗖ation 𝗰𝗼𝗺𝗽𝗲𝗹+𝗶𝘃𝗲 → comp𝗨𝗟𝗦ive
But—you may be thinking—none of the words I've listed so far are like Irregardless. All the words I mentioned have irregular *forms* (𝗿𝗮𝗯𝗯𝗶+𝗶𝗰 = rabbi𝗡ic) while Irregardless has an irregular *meaning*.
That is, regardless means "without consideration for". The suffix 𝗶𝗿- negates meanings (e.g., "irregular" means “not regular"), yet Irregardless means the same thing as Regardless. Surely that makes Irregardless different from other words, right? Wrong.
Recall that -𝗶𝗰 makes words into adjectives (icon→iconic). The suffix -𝗮𝗹 also makes words into adjectives (tide→tidal). Note that -𝗮𝗹 specifically does not combine with words that are already adjectives (sad→*sadal, strong→*strongal).
It turns out that there are a whole bunch of words that contain -ic and -al that seemingly shouldn't. Historical shouldn't exist because Historic is already an adjective. Cyclical shouldn't exist because Cyclic is already an adjective. And so on: Classical, Comical, Symmetrical
Words like Historical shouldn't exist because you shouldn't be able to add -al to words that are already adjectives, but here we are. They exist. And not only is nobody complaining about them, they are part of educated, formal language (not the "ignorant" speech of Irregardless).
In fact, one pleasant side effect of having both -ic and -ical words is that they express different shades of meaning. Historic means 'notable in history'; Historical means 'relating to history or past events'.
But wait, there's more. There are in fact other words in English (and the dictionary!) that are EXACTLY like Irregardless, yet nobody complains about them or bemoans the downfall of English through ignorance. Unloosen - to loosen Unthaw - to thaw Unravel - to ravel
In case you are unfamiliar with it, "ravel" literally means literally to. So Unravel and Ravel mean exactly the same thing.
(picture showing dictionary definition of ravel)
Lest you think there's been a sudden onslaught of insanity, each of these words has been around for hundred of years. David Hume even said them.
(picture showing citation)
So to sum up, Irregardless is not unique or even that unusual. There are plenty of words where the form and meaning of the whole is not the strict sum of its parts. And we just use them everyday without even noticing. One day no one will notice Irregardless as unusual, either.
Coda: when you take a descriptive view of language as linguists do, you start to see its beauty. As this M-W page describes, unloosen, unthaw, & unravel all have roots that seemingly have negation as part of their meaning (loosen means "make not tight").
(picture, link to M-W usage notes: 'Un-': You Don't Always Have to Be So Negative)
Interestingly Regardless also has a negative meaning! This suggests to me that there is something special about negation that makes it easy to combine multiple instances w/o changing the meaning (see also the widespread use of double negative syntactic constructions in languages)
So when one stops peeving and actually looks at the science of language, Irregardless is part of a particular systematicity in linguistic cognition rather than being some grotesque outlier. And personally, I think that’s beautiful.