I disagree; I've done that before when I've answered a question, because I felt another answer had appeared which was incorrect or misleading.
For example, I answered one question about some kind of 2d sorting issue - another answer popped up which was both incomplete (it only dealt with the 1d case, which was trivial) and incorrect (it claimed to run in linear time, but was blatantly using a nlogn sort). I felt that a downvote was the right thing to do - but that does rely on the honesty of the users, and it sounds like that's often lacking.
I disagree also (re: I'd have taken it a step further: if you provide an answer to a question, you shouldn't be allowed to downvote other answers to the same question.)
There's definitely a problem here and something needs to be done, but that's not the solution.
I wonder if something like displaying answers on newly asked questions, but locking voting for <x> minutes (where x=???), and total_answers < <y> wouldn't stop the answer sniping in its tracks and give people willing to put the proper amount of work into writing an answer an equal footing.
SO has proven that the community for some reason is more than willing to spend vast amounts of energy helping others in exchange for "karma", but from what I'm reading lately, they are somewhat in danger of letting the golden goose die (or, a lot of the golden gooses). It'll still be a great site, but it could be a lot better if they tightened some of these problems up. I think they might be focusing on other things now though.
For example, I answered one question about some kind of 2d sorting issue - another answer popped up which was both incomplete (it only dealt with the 1d case, which was trivial) and incorrect (it claimed to run in linear time, but was blatantly using a nlogn sort). I felt that a downvote was the right thing to do - but that does rely on the honesty of the users, and it sounds like that's often lacking.