Is voting to balance in the spirit of the site?
I've seen a few comments on questions or answers on SO along the lines of this:
Why was this downvoted (I upvoted to nullify)?
In this case, someone voted down a reasonable answer. Then someone else voted it up, but it appears from the comments (and this is just one example) that the second person would not have normally voted up this answer. The person only voted it up in this case to counter the down vote that he considered unwarranted.
Is this a reasonable thing to do? Is it ever appropriate to vote in response to someone else's vote rather than on the merits of the question/answer?