I read in the FAQs that voting is done to express agreement or disagreement over here:
On Meta Stack Overflow, voting is often used to express agreement or disagreement, not to point out a lack of quality or helpfulness. Please don't be concerned if you receive downvotes – members of the community may simply disagree with your bug, feature request, support issue, or the nature of the discussion.
Then why is there a rep threshold for down vote? The first thing that comes to mind is that if we allow down voting from the start, we may get trollers who would keep down voting stuff. However, there are other ways to deal with it. For example, we could check the activity of the user in the discussion (measure by number of questions/answers/comments and also number of times upvoted (this is different from rep)) before enabling this privilege.
Use Case(unfortunately my own):
When I first saw meta, I knew nothing of it and nothing about Area51 and got a lot of down votes for that question. I lost a lot of reputation for a starter that day and was paying for that first timers mistake for some time before I got that reputation back.
Please condider the discussion of thread as a feature request. I think there are mainly two suggestions from the various comments:
Remove down-voting all together
- Change the down-vote reputation threshold to 15(same as up votes)