Again we see that the Courts are saying that citizen groups do not have standing to support laws placed on the books by their elected officials.
Careful -- these are two separate cases with very different rulings. I don't think they're doing the stuff you're worried about.
The California Supreme Court ruled that anti-gay marriage legislation violated the state constitution. Prop 8 was a California ballot initiative that created a state constitutional amendment banning gay marriage, thus overriding the state courts. Two couples that were denied marriage licenses sued in a federal district court to overturn the amendment. They had standing because they were harmed by the amendment. State officials refused to defend the amendment, so citizen groups intervened and put up their own legal defense. The district court struck down Prop 8. Then (this is the important part), the *defendant-intervenors* appealed that decision to the Ninth Circuit Court. The circuit court asked the California Supreme Court whether the intervenors had standing under California law to appeal. The California court said yes, so the Ninth Circuit reviewed the case and affirmed the decision. The intervenors then appealed to the Supreme Court. What SCOTUS actually decided was that the Ninth Circuit should never have taken the case because the defendant-intervenors were not harmed by the district court's decision, and thus had no standing to appeal. To quote from the SCOTUS decision (emphasis mine):
The parties do not contest thatrespondents had standing to initiate this case against the Californiaofficials responsible for enforcing Proposition 8. But once the District Court issued its order, respondents no longer had any injury to redress, and the state officials chose not to appeal. The only individuals who sought to appeal were petitioners, who had intervened in the District Court, but they had not been ordered to do or refrain from doing anything. Their only interest was to vindicate the constitutional validity of a generally applicable California law. As this Court has repeatedly held, such a “generalized grievance”—no matter how sincere—is insufficient to confer standing. See Lujan v. Defenders of Wildlife, 504 U. S. 555, 573–574. Petitioners claim that the California Constitution and election laws give them a “ ‘unique,’ ‘special,’ and ‘distinct’ role in the initiative process,” Reply Brief 5, but that is only true during the process of enacting the law. Once Proposition 8 was approved, it became a duly enacted constitutional amendment. Petitioners have no role—special or otherwise—in its enforcement. They therefore have no “personal stake” in defending its enforcement that is distinguishable from the general interest of every California citizen. No matter how deeply committed petitioners may be to upholding Proposition 8, that is not a particularized interest sufficient to create a case or controversy under Article III.
So basically they said you can't ask a federal court to intervene in state law just for fun; you have to be actually harmed to have standing. The intervenors did, however, get to make their case at the district court, and did so quite thoroughly. (Thoroughly badly, that is, but given that there's no actual case against gay marriage...)
Meanwhile, in the DOMA case, the Supreme Court decided that the "citizen group" (actually the House of Representatives) did have standing to defend DOMA. While the Department of Justice (under Obama) did not actively defend the law, they did continue enforcing DOMA throughout the legal process, appealed each decision, and supported the House's standing. This seems to have been a deliberate strategy to give SCOTUS the final say on the law's constitutionality.
In both cases, the executives branches refused to defend the laws because they believed them to be unconstitutional, but continued enforcing the laws until the courts made a decision. That seems like the opposite of imperial to me.