Josh Marshall sums it up nicely in this post (link below). The only thing he leaves out is that if so many union members didn't vote Republican, we wouldn't have Republicans trying to bust unions. Show me one Democrat who's trying to bust a union. It's solely the GOP that goes after unions, and plenty of union members vote for them.
Just another case of voting against your interests coming back to bite you.
"Because of the Great Recession, tax revenues are down dramatically and public services costs have soared. Ergo, we have no choice but to permanently eliminate union rights for public employees. Because we're out of money."
- The Argument in a Nutshell | Talking Points Memo (view on Google Sidewiki)