Well, that's one of the reasons I don't correct people as a general rule. Even the best of writers can write a scrambled sentence when they're tired, people might be foreigners, or dyslexic, or distraught, or crumby typists. But if they are criticizing somebody else's English, they are fair game (and those posts always contain at least one error). And if they ask for input, I'll tell them straight that they need to learn the basics of grammar. Although I usually prefer to avoid responding. They rarely take it well, even if they asked. And if somebody asks if grammar matters, well, that's a subject near and dear to my heart. If you don't know the difference between you're and your or when you should use me and when you should use I, that won't prevent you from becoming a writer. But only because those things can be learned. Until you learn them, they will almost certainly prevent you from becoming a writer. And if that's where your weakness lies, you will do yourself an immense favour by trying to make every sentence you write grammatically correct, until you can do it as naturally as breathing. Because while industry professionals will take the occasional error in stride, there is no way they are going to take on a manuscript in which every other sentence is crippled. And I don't blame them one little bit. Life is too short and there are too many other writers who have made the effort.
All of the you's are meant as general terms. I'm not speaking to any particular individual. It's just a general principle. If you want to be a professional anything, you do what it takes to master the skills and knowledge necessary. And it shows, even when you're off-duty. A fashion model doesn't suddenly become fat and clumsy, just because she's wearing tattered jeans in her back yard. An athlete doesn't suddenly become uncoordinated on his day off. Their professional aptitude shines through, even when it's not on display. If you're writing incomprehensible slop, it's time for some basic drills.