But what the hell, let me just say a couple of words about the arguments you hear against unions all the time.
"Unions are corrupt!!"
All powerful organizations have corruption problems. Corporations, government. Why are unions so often singled out in this way? The image above I think explains it. But on the plus side unions are democratic. So there is at least a check on corruption. Corporations are tyrannies and governments often get captured and controlled by tyrannical corporations. So corruption in these cases can be more difficult to deal with.
"I know a lazy guy that should have been fired but the union protected him."
When you aren't a slave and you have some power sometimes you do things that aren't great because you can. This is not perfect, but the alternative is worse.
It's like a parent and child. In most healthy families sometimes children act up. Sometimes they don't do what they should. They get away with it because their parents love them and aren't going to crush them.
Unhealthy families can be different. For some families the children fear their parents and almost never disobey. When they go to church and all are at strict attention, never acting out, one might look at that and think it is admirable. But maybe it isn't. Maybe it's better when there is a little more balance, a little more equality in the power relation. The price of that equality is the children don't always do as they are told. They don't always do the right thing. But it's better this way. It's worth the price.
Salary negotiations should be left to the free market. That's why I oppose the fight for $15. You should only make $15 if you can command that salary based on market demands for your skill set.
Organizing and fighting for $15 is a free market activity. When Walmart wants to get a good price on paper towels they consolidate their purchasing power. Workers are doing the same. They are consolidating their labor in order to negotiate the best labor rate they can get. If it's good enough for Walmart it should be good enough for workers.