As a N-NS I am curious if everyone here thinks that downvote is effective for the learners.
It may appear that it is irrelevant. And at many times, a downvote may affect the morale of the learner. Not every learner can ask complete and high-quality questions. When all these are considered, downvotes may appear useless.
However, when somebody asks a question on ELL, it is seen by thousands of other learners too. So, when a question is of poor quality or when it is incomplete, an answer to it may mislead may learners. We do not want people to learn something wrong, now do we? A downvote may appear dis-heartening at many a times. But when a question or answer is downvoted, it makes it clear to a reader that this post needs a little more clarity, or it would be plainly incorrect.
I myself have been voted down many times. But instead of taking offence, I check my posts for ways to make it better. If I cannot do it, I may seek help from any of the experts here, for there are plenty and they are always available to help you. I have seen many people edit my posts and that edit converts my downvoted question to a popular one, if the question is worth having an audience. Downvotes are not here to criticize anybody's questions or answers, but only to flag it as a post that may need a little more clarity, or have been asked or answered before.
To avoid downvotes, or any actions that may end up closing your post to the public, avoid posting contents such as:
Posts that are really unrelated to what this community is all about. They may get voted down, or could even be closed.
Posts that are include very basic things that you could learn with a minimum effort, say a simple Google search or a dictionary reference.
Posts that are completely incomprehensible by multiple users.
Posts that have been posted by some other users, at some early point of time.
Posts that are rude or offensive.
Proofreading posts that clearly ask for corrective suggestions.
Posts that contains extracts without proper reference.
Posts that contain very low quality, not sufficient content to make it clear.
There are many, many more. Just keep in mind that you ask or answer something with utmost clarity. If you're not sure, do seek help. You could ask somebody to edit the question for you as a post script in your original post too.
So in short, everybody here wants to help. Downvotes are very useful. Help us to help you. Cheers !