I've worked at a non-union airline, and I will NEVER again put myself in that position.
By allowing people to not be a part of the union (and not pay), all the corporations are doing is allowing the union to lose power. This is why every single private sector job has less and less union membership. "Oh but why do I pay the union since I work under the same contract anyway"
Exactly, why would you? Not seeing that in the long term the union loses its power.
And remember this: The union isn't only there to protect you from the company, it's there the protect you from each other as well.