Chances are excellent that you are mistaken about English grammar

 One way to get the morning off to a strong start is to open an online discussion of grammar and growl,  realizing that many people hold strong opinions that are wrong. So rather than wear out my wrists responding to them, I am writing an omnibus response to uninformed opinions so that I can simply post a link and move on. 

No one knows how to use proper grammar these days.

I edited the work of professional journalists at daily newspapers for forty years and taught editing at a liberal arts college for twenty-five, and I can assure you that just about no one got the grammar straight. Every shift, every class involved making subjects and verbs agree, putting modifiers in their proper place, sorting out homonyms. Writing formal standard English is a skill that not many people master, and not many ever have. 

The English language is in decline.

English is a living language and has been going strong for centuries. There are, in fact, many Englishes, and the various dialects are not inferior to standard English, just used for different purposes. Usually  fuming about decline comes down to some nonstandard usage or dialect or particular word that the commenter has taken a dislike to. 

I regret to inform you that English does not care what you like or dislike. 

What you see is that the internet permits anyone who has a keyboard and a link to display their skill or lack of skill in writing to the world. Most of the gatekeepers to publication are gone, like the editors on vanished copy desks, and for the first time, as Gretchen McCulloch explains in Because Internet, the whole range of literacy in the populace is visible. 

No one is teaching grammar.

This one boils down to a belief that the traditional schoolroom grammar, relentlessly hammered in, is the only proper method of instruction. 

In elementary school in rural Kentucky, I was instructed in that schoolroom grammar by the formidable Mrs. Jessie Perkins and the equally formidable Mrs. Elizabeth Craig, and I mastered it. Evidence suggests that not many of my classmates did. The method is only effective with a minority of students, like sentence diagramming: Students who already have an understanding of syntax love it; students who do not learn little or nothing from it.

The further problem with the schoolroom grammar of elementary and secondary schools is that it is grossly oversimplified, and not many students advance to a more sophisticated understanding. It is also riddled with obsolete dicta and superstitions. This is why, a century after the Blessed Henry Watson Fowler exploded the prohibition about split infinitives, you can still find people carrying on about this imaginary error. 

Some schools, recognizing the ineffectiveness of the traditional method, have tried others. One approach is to say that since many subjects require writing, all the teachers in those subjects are effectively instructing their students in grammar and usage. But we know that what is everyone's job is actually no one's job. 

I found in teaching that many students came to me with little or no instruction in grammar and usage, and that those who had been instructed had often been taught rubbish. 

It was acquaintance with linguists and lexicographers that helped me to finally unlearn the defective or inadequate learning I had so painstakingly acquired. 

Maybe think before you post.

You think it's incorrect to end a sentence with a preposition? Use literally in the nonliteral sense or use hopefully to mean "it is hoped that"?  Seeing or hearing some particular word is "like fingernails on a chalkboard"? (Not the most original simile you could have laid hands on.) 

I remind you that Garner's Modern English Usage by Bryan A. Garner (for reasonably informed prescriptivism), Merriam-Webster's Dictionary of English Usage (for historical perspective and range of choices), and Dreyer's English by Benjamin Dreyer (for bracing advice) are in the stores. You could look it up. There's a lot in English, and even standard English has more choices than you may be aware of. 

A final note

I included a split infinitive and a singular their in this post. If you read past them, then you can see that they are imaginary errors. If you did notice them and were inclined to remark on them, get a life.