A decent union is mostly about job conditions, not job security - collective bargaining prevents a "race to the bottom" where abusive conditions creep in due to there always being some people who'll do the job anyway. A good example is the Screen Actors Guild which imposes all kinds of minimum conditions, for example, due to which all kinds of safety issues in filming are handled quite decently (even if stuff does still happen), despite the fact that many desperate wannabe actors would easily sign a contract where they agree to whatever conditions the company imposes.