That's not the case with pilot or F/A groups at the airlines. Look at F/As, they're easily replaced. I guarantee you that the company does NOT CARE if people leave in droves.
That was the case at ACE, but after 3 captains and about 4 FOs left in a 6 month period they changed the pay scale, and allowed FOs to upgrade quicker. That solved the problem temporarily, the issue with "pilot pushing" will probably raise its ugly head after awhile.
Speaking of pilot pushing, a union is not there to protect you from it. That's you're own job. If you don't think you should go, then don't go. A union isn't the way to deal with that. Dealing with pilot pushing should be a part of your intestinal fortitude, and something that goes down in the Flight Discipline category. It shouldn't be "I don't have to make this trip because I'm uncomfortable, and the union says I don't have to if I'm uncomfortable," it should be "I am not going to make this trip because I don't think these conditions are condusive to safe operations."
The only valuable attribute of the union is your protections. They really aren't that much, but you get to know that if you're fired for unlawful reasons, you will be protected to an extend. Frankly, the dues are a cheap insurance, however I think that the current system of seniority is a joke, and pay scales for starting FOs are insulting. Is there work that needs to be done? Yes. Are people doing it? Yes.
Finally, someone said your job is not to be a good pilot, but to be a robot, and mechanical standardization machine, automata, whatever. Frankly, I think this is delusional. Thinking for yourself in the cockpit is the most critical attribute of the pilot. That doesn't mean you will do things that aren't standardized, but the emphasis seems to be on the meat-puppet aspect of flying and not on what counts - Airmanship. A pilot unthinkingly follows the checklists and procedures in order to control the airplane. An airman follows the checklists and procedures in order to safely and efficiently control the airplane. Checklists and procedures are there for a reason, but think about the reasons behind your actions.