So that's one reason to have standing: we want the court to deal with an actual adversarial context, or else people might miss their chance to assert their rights, because their case might have been decided in advance.
We want a context for saying what the law is. Note, by the way, that for standing, we're just dealing with one side's characterization of the facts. So when we say we need adversaries and we need facts, it's not quite facts-- it's more like pleadings: assertions about what facts will be proved and how.
Note that in MA v. EPA the only reason there is standing is that the court buys into the plaintiff's assertion of what global warming will bring.
The best plan is to have the executive take a position about what executive power should be (i.e., what the law is), and save the court as a reviewing body until an actual controversy arrises.
Are advisory opinions such a wholly bad idea, though? Some states allow them, for example, and the founders did at least consider the idea of a Council of Revision. But we're nervy about advisory opinions because it puts the courts too closely aligned with the execitive. At the same time, though, the court could at least look out for the interests of the party not present, instead of just leaving it up to the executive to pick a policy position. Still, it's kind of an ex parte communication, and there are procedural reasons not to have it.
Courts are good at telling us what the law is, because they do so in the context of particular facts. They might not be so good at telling us stuff if they are reasoning in the abstract.
And hey look: all cases are advisory. That's what stare decisis is. And in fact SCOTUS grants cert because deciding some case would be useful in deciding others. And we're OK with dicta (60% of Marbury is dicta, after all). So maybe the no advisory opinion rule is really about not piling work onto the courts. A resource management argument could be made, at least.
See p. 36: comparison of Allen v. Wright and Duke Power Co. v. Columbia Environmental Study Group, Inc. In Allen, the problem was that white parents were pulling their kids out of desegregated schools, and that this was enabled by the IRS not denying tax exemption for racially discriminatory private schools. In Duke Power, the company wanted to build a nuke plant, and wanted to be sure that federal limitations on liability for nuke accidents weren't violative of due process. Standing in Duke (for people wanting to prevent the construction, not because of the power plant's hoping for a ruling) but not in Allen. But that's a pretty thin injury in fact in Duke: if the plant were built, the water would be warmed and some fish would die. Maybe what was really going on is that the court wanted to help out the power plant by declaring the law, and in the school case they didn't want to meddle in federal tax policy. And they used standing doctrine to ccomplish what they wanted. So we can suspect that the doctrine's application correlates with the court's opinion of the issue or the litigants.
Some conflict here between reason and rationale, in other words. And maybe what is really happening isn't even legitimate, in the sense that the underlying reason might be just fine (i.e., we think granting this relief is actually worse than the problem it purports to redress), but it's being wallpapered over with this doctrine of standing in order to avoid having a frank discussion of something that seems beyond judicial empowerment or competence.
But we don't want the "ideological plaintiff:" someone who says they're hurt just by seeing the government not being vigorous enough about following the law.
So maybe the doctrine is really being applied, after all. Maybe we just perceive political reasoning because of our own political view of the policy issues at stake.
Still, what's the big deal about being a state? Why should the injury in fact test be relaxed? And there's nothing about the decision that rests on that relaxation: MA is just a landowner, really.
Maybe the court is getting a little activist about global warming. They're getting political and finding an injury, perhaps. And even if you buy the injury, causation (EPA did not cause global warming), and redress are even harder to find.