As a lawyer, I agree with you whole heartedly. Just because a legal decision recites a sound legal argument doesn't mean that that's the only sound legal argument they could have made. In the same way that a competent lawyer can make the best arguments for either side of a case, a judge could write multiple opinions for the same case that have different outcomes. And all could be just as legitimate from a logic and legal standpoint. But the judge chooses what opinion to write and what outcome they want. All of this makes the study of law kind of silly, because you study a bunch of case law and pretend that there's consistency or logic that ties them together, but really it's largely driven by the individual personalities more than some platonic ideal of what the law should be. It's a liberal art, not a science.