How long have you been here to be a mapmod and not know these things? There are a number of reasons people vote a map down and the consensus opinion among most experienced (long-time) players here is that down-voted maps fall into two categories. One is basically sucky maps that nobody likes, the other is hard maps that have a trick to completing them. Many players will vote a map down if they get killed trying to beat it. The latter category usually gets a few positive comments, use the comments as a guide to decide if you make a bad map or just a map for experienced/expert players.
Even Teknotis complained at a map I made once, just because I called it "nothing special" and he thought it was hard. That particular map got like 60 down votes. I survived.
But you should know that I fully support an open voting system where people can vote on maps even if you are not a forum member. There is no reason to have to create a forum id just so you can vote on a map in a game you purchased. Also, you should be able to vote on a map you have not completed, since it may be a bad map (for you, at least) and you have a right to express that opinion. One should not be forced to play a bad map just to be able to say it is a bad map.
But these arguments were conducted a long time back, more than once. They are still here in the forum if you care to read back. Which you probably should do, rather than proposing the same old "fix" that has been discussed and rejected a long time back.
'If you want to live a happy life, tie it to a goal, not to people or things.'
Albert Einstein
(1879-1955)