Jonathan Adler has a nice post on standing over at Volokh.
Here is my contribution to the standing issue:
1. They have standing. The requirements for standing (stated simply)are injury, causation and redressability. You can’t say they don’t have an injury — they raised millions of dollars, got an initiative on the ballot, worked thousands of hours to promote and get Prop 8 passed. Now, a plaintiff comes around that wants to undo all of their work and reverse the whole process. They certainly have an identifiable interest in preventing the unraveling of all they have accomplished. Their harm was caused by the plaintiffs filing of the suit and the judge’s decision. And a court can effective redress their wrong. In other words, as one commenter noted, standing is generally something that applies to plaintiffs ability to bring the case in the first instance. However, once a case has been brought and has resulted in the curtailment or elimination of a definable right previously “owned” by the defendent, that defendant has standing.
2. Californis law requires that initiatives be “sponsored” and creates a specific category of individual called a “official sponsor” of the inititive. These sponsors essentially stand in the place of governmental officials who have refused to, or have not, passed legislation to address the matter. So Prop 8 proponents are not simply members of the public with no other definable interest in the matter other than their membership in the general public; they are people with a quasi-governmental status, created by California law. They have a special definable interest in seeing Prop 8 be enforced, and not cast aside because of the very unusual circumstances of this case which are…
3. That the responsible officials who are supposed to defend the state constitution are refusing to do so. That fact makes a big difference.
Now, there are cases that might run contrary to this general thought on standing: Arizonans for Official English might have something relevant to say. I haven’t read that one yet. And there was one other case cited by Judge Walker that was an appeals court case.
But I think the critical thing here is that it is an initiative, that the normal governmental officials have refused to defend it, ( which is a good way of governmental officials killing off initiatives) and that the sponsors are not just members of the public.