When the Justices extend the hypothetical (a practice Justice Breyer particularly enjoys), what they’re doing is trying out different ways of looking at the law in situations that might arise sometime in the future. That’s because they know that their decision will apply not only to the facts of the case currently before them, but also to lots of other cases in the future. They want to make sure that whatever they decide about what the language of the statute means will work in all (or at least the majority of) these cases, even though they have not yet arisen. Sounds hard, right? But that’s part of the job of a Justice: to look into the future and think about what other kinds of cases are down the pike.
Lawyers understand this intuitively after several years studying appellate case law and years more on the job using it and advocating within the gray areas of the law. But, the rhetoric of judicial philosophy and judicial appointments often obscures the basic fact that appellate court cases almost always impact not just the current case but future cases by setting forth a policy in a set of facts where the law might otherwise be ambiguous.
A great deal of harm can result from reaching the right decision for the wrong reason in an appellate court decision, because it can produce the wrong results in many future cases with different facts. A judge who fails to consider the future implications of a decision, however, is more likely to make the right decision for the wrong reason. But, this farsightedness in drafting the right rule for all or most future cases based on the law can look like naked policy making based on personal perference to those who don't intuitively understand how precedents impact future cases.
All appellate court cases make policy. The question is not whether a judge makes policy or not, but whether the judge makes policy in a principled or unprincipled manner.
This is particularly true at the top of the appellate judicial food chain, where courts have discretionary dockets and don't agree to even consider or issue opinions in the unambiguous easy cases that lower appellate courts have already resolved correctly. These cases, almost by definition, can be resolved in more than one way and have an important impact on future cases. And, top of the judicial food chain courts are also in a position where it is difficult or impossible to correct their mistakes.