Well yes, if someone were to ask me, then I'd help (always assuming I knew enough to help), but my experience of forums suggests that many, perhaps most, people don't want to be corrected. I've never dared anyway, but I've seen such furious reactions that I'll continue to leave well alone (and learn).

Of course, people whose first language is not English are far more likely to be positive about offered corrections, but I would still wait to be asked. In any case I am neither a professional writer nor a teacher, so my opinions are not always reliable.