HN user jfc said it better here: https://news.ycombinator.com/item?id=7650975
Moreover, jfc has valid points about negativity and unhelpful responses, but it remains anecdotal. As a counter, my own anecdotal experience has largely been positive on SO, and I rarely run into those problems. I am definitely not part of the cohort that was there first, and think it's a rather fair system. For example, preventing downvotes until a certain level of reputation is reached is a small check on those looking to farm karma by blanketing out competing answers. Obviously it isn't foolproof, but it at least ensures that you have actually contributed to the community at least a few times.
Perhaps his comment speaks more to the quality of the userbase than to the efficiency of the voting system?