It doesn't get any better

I blog here. I blog there. I try to get people to realise that the singular of criteria is criterion but it is so uphill. Even teachers of English are arguing that usage has changed that "a criteria" is now correct English. However, even though this usage has been around for 50 years, I have founf no dictionary that supports this. As far as I can see, the use of "a criteria" is still illiterate.
Oddly though Meriam-Webster seems to recognise the non-word "irregardless" as having the right to exist through usage, even though noting it as a poor verbal usage and not recommended in written English.
Mind you, none of us avoid a fall completely. Earlier, I used the phrase "so uphill" like a teenage fan of Buffy the Vampire Slayer!
Please help protect our language!