I'm sorry you are having troubles, jmitw. We all have some sort of problem and yours happens to be this. I didn't want you to think that the rest of this post is about you.
English is a language that always presents something else to learn. I am very good in grammar and spelling. I believe there is still room for me to learn more about grammar and spelling all the time. Even dialect makes a difference.
Just for the others who are careless or don't think that there is always something new to learn each day, I wish you would stop complaining about Grammar Police. As long as the person is trying to be helpful and polite, accept the correction. Here and on Facebook, and having lunch with friends, that's a big way I can learn.
I think that Grammar Police serve an extremely useful position. Think of it this way. Most of us are visual learners. I think that most good spellers are visual learners. If someone misspells something or uses bad grammar, people see it that way quite a bit and then begin to think that it is the correct usage. It is better to have good grammar and spelling because it helps others. In other words, you are being a good example. I've never noticed anyone making that kind of point, but it has always been important to me.
We learn from others here all the time. Let the Grammar Police help you all, too. I'm sure that some of them can help me as well.