it's tricky...
Unions are pretty shady - they influence elections, they do some shady shit with the $, lots of accusations of bribing, etc - They take a lot of dues and do a lot of things most people would call shady. So on the macro, BAD.
On the other hand, for individuals, those that join unions do get higher wagers.
http://blogs.ajc.com/business-beat/2012/12/12/across-the-board-union-workers-get-higher-pay/Micro, it's good.
Government workers: “These workers make a median of $973 a week, roughly $230 more than their non-union counterparts.”
Teachers: “The union members earn $224 a week more than non-union educators, with median weekly earnings at $1,038.”
Firefighters and police officers: “Union workers make about $1,008 a week, and non-union workers make $627.”
Factory workers: “Union workers make about $836 a week, $56 a week more than non-union employees.”
Construction workers: “Union workers earn about $361 more per week than their non-union counterparts.”
Transportation and warehousing workers: “Union employees earn about $215 more per week, or 30%, than non-union workers.”
Utilities workers: “Union employees in this industry tend to earn 10.2% more per week than non-union workers.”
So if you are a worker, then yes, you like them.
If you're not a worker, and you don't make X amount more because of them (OR, if you are negatively affected by their practices or the higher wages given), then you are definitely against them.
It's not a right/wrong... that all depends on WHO you are.