I have never had any direct involvement with unions. However, my neighbor is a Northwest Airlines mechanic and their union was essentially "busted" recently (although the union still exists and some members remain on strike). His main complaint (as well as many of his fellow mechanics) was that the union management received at least 3 proposals from NWA and NOT ONCE did they allow the members to vote on them. Each proposal got worse and worse for the union workers and NWA eventually filled all the available positions with replacement workers and union members who chose to cross the picket lines. After a number of months, they were allowed to vote on a proposal once NWA had essentially filled all the mechanics positions and would essentially allow the mechanics who were still striking to get unemployment benefits (as well as some other things). That proposal was voted down and it seems sad to still see a few picketers still at the airport. In this instance, the union management hedged all of their bets that NWA would be unable to maintain their schedule using the replacement mechanics or that there would be some sort of major mechanical related issue with a plane or planes. NWA was able to continue operations and nothing major has yet occurred regarding airplane safety.
I am a member of three unions. They are what I would consider bad, medium, and good. The AEA is pretty bad, if you ask me. They do get actors some benefits and safe conditions that are necessary, but they make it overly difficult to mount productions. The level of injustices against the actors in productions under AEA jurisdiction isn't all that great to begin with. So they aren't totally necessary. SAG, is in the middle. They have some conditions which are just silly. But there is a high level of people who take advantage or would if they could in SAG productions. SAG is necessary to protect the talent. Otherwise they would be screwed over constantly. It is just too bad that SAG also has quite a few frivilous demands in their contracts. In LA I am part of the teachers union. It is both necessary to protect teachers, and great, because they really do hold teachers to high standards. They have even proposed things that help to put some type of teacher quality control in place, by having the teaching standards, which was an initiative from the union rather than management. They are also needed to protect teachers who are often overlooked in the education cycle. I have heard that other teachers unions aren't so great, but the one I belong to, is amazing, and does a real service not only for teatures, but the students they teach.
The NWA mechanics union IMO badly misjudged their position. Being a union doesn't free the company from the business cycle and if unions have to realize how much the company can afford to pay them. If you look at the Delta and American Airlines unions all of their unions realized that those companies couldn't survive with the current arrangements and if the unions wanted to keep people working they had to renegotiate contracts even if it meant less, benefits and job security for the employees. The NWA mechanics just never seemed to understand that and got screwed over. When the other NWA unions wouldn't join the mechanics in a walkout that should've been the big clue to the mechanics that their strike wouldn't succeed.