Yeah, you know, we also tend to wonder offtopic (see what I mean? we're offtopic), and it's not always clear that we've done that. There are people here with very strong convictions that will frequently look like they're pushing them onto us, even when they're not. (I think I'm one of those people)
Anyway, iceman's right, you've gotta be able to tell someone to **** off. That's something that's true all over the internet, and I personally think is true in real life. I'd add that you've gotta be able to call bullshit too when someone's posting bullshit. But both of these attitudes are considered "impolite" by so-called "polite society", and you may not be wired to do that sort of thing.
Otherwise, on grammar, it's just plain rude to attack someone's grammar under circumstances like these. We're an international group, so attacking someone's English is going to be pretty rude. There are exceptions (like when Jonathan attacks my grammar, I consider that an exception, I don't think he's a native English speaker, but his English is really good, and I am a native English speaker with high standards for what I write), but not many.
And most importantly, don't feel bad about leaving a small post if you just don't have time to write a longer one.

What makes me personally feel really bad, since I tend to write long posts (and long emails, this happens most in email) is when someone tells me it took them hours to read my post because their English wasn't up to the task, and then it took hours for them to respond, because I don't know their language. I can't think of anything I have to say that is so important that someone should spend that kind of time on it, really.