The other day I argued for ain't as a fine Anglo-Saxon word. Herewith some further considerations.
You'll notice that we have many contractions for various forms of "to be" in English:
Sure, one could insist that others use "I'm not" rather than "I ain't", but then why not insist on "we're not" rather than "we aren't", "it's not" rather than "it isn't", and so on down the line? I see no good reason to disqualify "ain't" on grammatical grounds.
(I know, accepting "ain't" may seem like lowdown linguistic latitudinarianism to you grammatical prescriptivists out there -- you know who you are! -- but personally I see it more as a return to our Anglo-Saxon roots. What's next, you ask? Will I come out in favor of "y'all"? Only time will tell...)
Peter Saint-Andre > Journal