Public unions like pensions because they are defined benefit plans and are guaranteed a specific monthly benefit. The risk is passed to the tax payers because they need to cover any poor investments.
Let me rephrase. I don't understand why union members feel comfortable trusting a large portion of their employment benefits to the whims of the legislatures or much more rarely now, private companies, that "garauntee" them, nor to the capabilities of the pension manager. The downside of lack of mobility, lack of choice, and poor performance all seem like they would be deal breakers to me, but again, I've never worked in a pension system.
Defined benefit plans can of course be had without using a pension so that seems a red herring.
