Personal experience with unions. The unions at Boeing protect workers who do drugs and sleep on the job. The teamsters union in Boston prevented my small company from unloading a small amount of equipment from our truck ourselves(enforced with veiled threats). The longshoreman's union hands out jobs to well connected members and runs a racket.

I'm not saying all unions are bad. I think many industries might benefit from well run, transparent, regulated unions. But I have seen many examples where they are bad.