It feels so narrow, almost like the author hasn't met enough people in their life.
People get grammar wrong all the time for many different reasons that are not always "logical": tiredness, loss of focus, focus elsewhere (on the actual content, for instance), dys-something, lack of sleep, something else. And for some reasons, it's not always easy to spot our own mistakes when proofreading. But that's a very well-known fact.
I myself make a lot of mistakes when writing even when I'm pretty sensitive to grammar and pretty good at it. And many very clever people don't seem to be wired for liking / being sensitive to grammar as much as I am.
By not hiring people who make grammar mistakes, you are missing out on great people. Your loss, I guess.
I guess it makes sense to hire people able to write well in writing jobs, but even then, if you need error-free texts, the only way is proofreading by other people and good tooling. So… unless the person does a lot of mistakes without being able to fix them… meh?
Also, I very much prefer reading a text full of mistakes but of which I can follow the logic, than an error-free text that I can't follow.
Maybe a better solution is to make society more tolerant to mistakes when reading? Saying this as somebody who' reading is easily disrupted by writing errors in others' writings.