Has punishment for precedent-setting decisions ever been recognized as retroactive enforcement of a new law?

Question

When a court sets a precedent, it is effectively creating a law (case law). This means that the law (or a newly clear interpretation that can only now be relied on) did not exist prior to the courts opinion being handed down.

If that is the case, it is trivially obvious that the person found guilty in such a "test case" could not possibly have broken the law, since the law is created at the moment of the decision.

Given that it is also clearly improper to hold someone responsible for laws that don't yet exist (violation of the "due process" clause), shouldn't those involved in test cases be protected from punishment? Are there any jurisdictions, or has there ever been a time, where "test case" defendants (and/or litigants in civil actions) are protected from punishment if a precedent is set from the decision? If not for the "due process reasons" but to encourage test cases that can improve the law—vs. the current approach which acts to prevent test cases because they are so risky. Has there ever been an attempt to implement such immunity, and if so, why/how was it defeated? Has a prosecutor and/or judge ever used their discretion to decrease or prevent punishment in a precedent-setting case?

Answer 1

Your premise that "the law did not exist previously" is, from the perspective of how courts work, mistaken. The law always existed, it's just that some people (maybe even judges) mistakenly thought the law didn't exist (actually, "meant something else"). Many people have wrong ideas about what the law says, but ignorance of misunderstanding of the law is no excuse. Even having an understandable wrong belief is no excuse.

There is an area in which ignorance of the law is excused. Violation of a person's civil rights under color of law is a civil wrong for which the officer can be sued. See Hope v. Pelzer, 536 U.S. 730 and citations therein:

Respondents may nevertheless be shielded from liability for their constitutionally impermissible conduct if their actions did not violate "clearly established statutory or constitutional rights of which a reasonable person would have known."

Thus an officer may not use a qualified immunity defense if the court finds that an action is a civil rights violation and this "clarification" of the law is new.