To start. My name is John, and I am a recovering stickler. As a bookworm and teacher's pet, I absorbed the schoolroom grammar to the last jot and tittle, and I was obnoxious about it. When you lack physical beauty, wealth, or distinguished lineage, you make use of whatever you can, and grammar enabled me to be an insufferable snob well into adulthood.
This is my first count against people who identify as sticklers: their weaponization of language to assert dominance. Telltale indications are remarks about "illiterates," "the masses," "hoi polloi," "the uneducated," &c., &c. But, as I have said before, snobbery about language is not more noble than any other form of snobbery; it's just a shabby little stratagem to gain advantage over others. Not just shabby, but a pathetic assertion of superiority, as when someone sports an "I am silently correcting your grammar" mug or T-shirt.
My second count against sticklers is that they are frequently WRONG. They will fume about split infinitives or none used as a plural or other bogus rules enumerated in my little book Bad Advice. They will complain that irregardless is not a word. They will carry on about terminal prepositions. And all that H.W. Fowler, the editors of Merriam-Webster's Dictionary of English Usage, Bryan A. Garner, and Benjamin Dreyer demonstrate to the contrary is pointless because Somebody Told Them Once and they will hold on to it until the universe enters its final entropy.
My third count is that sticklers refuse to acknowledge register, usually under the mistaken belief that formal written English is the only "correct" English, all other dialects and variants being defective and used only by "illiterates," "the masses," "hoi polloi," "the uneducated," &c., &c. All the Englishes, formal and colloquial, allow speakers within their respective communities of usage engage with one another. None is inherently more correct than the others, but more appropriate to the situation.
This is not to say that "anything goes," one of those ill-informed retorts sticklers are fond of, though I tend to endorse Flannery O'Connor's remark that "You can do anything you can get away with, but nobody has ever gotten away with much." I have been a professional editor for more than forty years and a blogger about language for eighteen, during which time I have learned many things and have found it necessary, helped by colleagues, linguists, and lexicographers, to unlearn several.
A person who did not leave a name commented on one of my recent posts, sneering about "those bogus rules that provided you a profession, but that you sanctimoniously deprecate." Yes, I enforced many bogus rules until I learned better, liberating myself and the texts I worked on from the stickler straitjacket. It turns out to be possible to produce effective language by paying attention to it and avoiding sticklers' faulty precision.