I no longer have a dog in this fight as I am retired--thank God. I have been in the military where everyone is paid by rank, work for a non-union airline with no real seniority system, and worked for a union airline with a strict seniority system. I would choose the seniority system. Without it it is too easy for management to play favorites. The guys who take the illegal assignments and fly the broken airplanes are the ones who get the good schedules and early upgrades. It does nothing for the quality of pilots. In fact it makes it easier to protect the weak ones if they are friends with the chief pilot. People are all looking out for themselves so junior guys don't like seniority and senior guys like it. Just the way of the world. As far as seniority allowing management to erode pay and benefits that just means you have a crap union.