Except… in most fields, when we want to find out how something works, we examine the evidence. We don't believe something just because someone tells us to believe it. But when it comes to language, we ignore the evidence and we believe whatever we’re told. After all, what else is “proper grammar”, besides a series of prescriptions usually motivated by nothing more than ipse dixit.
Take this guide to commonly misused words. This is from the entry on hopefully:
This word is used incorrectly so much (including by me) it may be too late. But let’s make you smarter anyway.
How can believing something simply because someone told you to believe it make you smarter?
Or 20 Common Grammar Mistakes That (Almost) Everyone Makes - if almost everyone makes them, how can they be mistakes? As motivated grammar says, one of these things is not true.
As an example of how we ignore the evidence, look at the rule for which and that from the "20 Common Grammar Mistakes" article. I wrote about this a while ago. Quite simply, the claim that which cannot be used with restrictive relative clauses is false. It doesn't describe how the English language works.
I also wrote about fewer and less: less can be used with count nouns and has been used with count nouns for 1000 years.
Or anxious: anxious has been used without any connotation of anxiety by some of the best writers of English.
This Grammar Day, treat grammar just like any other field of inquiry. Have a look at the evidence - I recommend starting with Merriam-Webster's Dictionary of English Usage - and make up your own mind.
* for the record, I personally don't hate George Lucas, and I don't love proper grammar. Maybe I should hand in my Original Geeksta card.