Yes, I know there ain't any such word as ain't, but due to colloquial acceptance of the word, the expression, "ain't what it used to be," has become so familiar that correcting ain't to isn't, grates on the ears.
What once was, ain't no more. I'm talking about a sin against the second commandment. Back in the day, it was almost socially acceptable to hear God's name taken in vain. It seemed the conversation was peppered with Christ! I even remember a comedian saying that until he went to school and everyone used the name his mother gave him, he didn't recognize it because he thought he was Jesus Christ. That's because every time his father saw him, he'd yell Jesus Christ!...
I used to think that maybe the habit arose because people were used to praying pious ejaculations and when surprised or something needed emphasis, they'd absentmindedly exclaim Mother of God!, or Jesus, Mary, and Joseph! How about, "Oh, for Christ's sake!" I can see where these punctuated expressions could also be used as prayerful ejaculations during the day and since these expressions of prayers were so readily on your lips, they shot out unexpectedly. Yes, I give people the benefit of doubt.
But they were considered blasphemous because you were using God's name in vain and/or disrespecting sacred persons. Not so today.
I contend that nowadays, in our very secular society where God is barely on one's mind, using His name in speech isn't thought of, even using the name in vain. It's like God never existed. He's out of sight; He's out of mind; His name is not even used to blaspheme. It's strange. Bad words like ain't are "in" and sacred names are "out." Correct English isn't a consideration any more than God is.