Two things:
1) What's going on in WI has nothing to do with balancing their budget. The unions have already made the financial concessions being asked for, so that's a non-issue. What it's about is eliminating the Democratic Party's biggest power base, the unions. It's a power-grab.
2) Regardless of #1 and whether or not you agree with the legislation, what those senators are doing is just plain wrong. I personally disagree with this piece of legislation, but I disagree even more strongly with the tactics being used to block it. If you feel passionately that a piece of legislation is wrong, you seek to undo it once it's passed, you don't paralyze your government so that it can't be passed in the first place.