Unions - Your Opinion?

If you happened to stumble upon this blog, please comment on your thought on labor unions in Canada. Is this another battle between conservatism and liberalism?
From what I have heard through people that I have worked with in the past, the ups of unions are that they protect workers from bosses who have the power to blackmail them by demanding unfair requests such as working too many hours in a row or not having breaks. The downside that has been expressed to me is that workers who do not provide quality labor are still guaranteed to get job security even though they bring down the coorporation, due to all of the rules about reasons for firing an employee.