But does adding the ir do the same to regardless as it does to resolute? Someone who is irresolute is not resolute. So if some one does something irregardless of danger, does that mean that they are doing it while taking significant note of the danger involved? If that's what it means it might be quite a useful addition to the language, indicating a higher degree of bravery for example - but my impression is that people mean the same by irregardless as by regardless, and it seems a bit redundant.

Another word pair where the words are synomyms in spite of appearances is valuable and invaluable. It is a weird language we share.