In S.F., without changes, around $500 million a year will be spent paying city employees who no longer work. That means the City will not have $500 million a year to spend on new jobs, welfare, parks and recreation, community programs, or attracting small businesses to S.F.
Using taxes to favor gov workers, especially people who no longer work, has severe consequences for any state that wants to remain competitive. For instance, in 2007, 6% of California's population moved out of state, according to the Pew Center. Many CEOs will not expand in California, citing ABC: "Anywhere But California."
At the end of the day, corporations must be responsive to you and me; otherwise, they will not be able to sell their products and will go bankrupt. Government unions, in contrast, do not need us. Given low voter turnout, unions can effectively deliver 20%+ of votes in local elections to the politician of their choice. Then, unions can use their politicians to increase their benefits on the back end--i.e., pensions, lifetime medical benefits, etc.--where the bill doesn't come due for many decades and becomes another politician's and perhaps even another generation's problem.
The backending of gov employee compensation destroys accountability, because it allows politicians to make ironclad promises that do not activate during their term. For gov unions, the advantage of back-ending gov employee compensation is twofold: first, voters do not see any immediate consequences and think everything is fine; and second, unions can continue to pursue a deliberate strategy of keeping younger, newer employees underpaid so they can use them as propaganda tools, even as their retirees receive unpredictably high and unsustainable compensation. Who suffers the most? Newer and younger people, whom politicians usually ignore because of their low voter turnout and naivete in supporting teachers, police officers, firefighters and other gov employees at any cost.
More on union influence here: http://volokh.com/2010/01/
Bonus: Will Wilkinson writes an excellent piece on government unions--see here ("Bad Bargain").