What happens if an IRB mistakenly approves unethical research?
Since researchers are not allowed to trust their own understanding and must seek IRB approval even in the most obvious "there's no way that could be unethical" scenarios, it stands to reason that the opposite is true - that if research has been IRB approved, then researchers may go ahead with a clear conscience even if they personally feel that the research still has ethical issues.


I don't see it that way.  The IRB doesn't replace the author's judgment, it supplements it, and the ultimate decision should be based on the "logical AND" of the author's and IRB's approval.

Since conducting unethical research seems clearly worse than not conducting ethical research (a Type II error is worse here than a Type I error), it makes sense to have an asymmetry between approval and rejection.

So in my view, even if the IRB has approved the research, the author should not go ahead if they do not believe it is ethical.


  If research turns out to be unethical, but it received IRB approval, who is held responsible? Is it solely the responsibility of the IRB for misguiding researchers, or does the researcher bear some responsibility for not recognizing the ethical infirmity?


Practically speaking, the researcher would have some cover because of the IRB approval, but I would still hold the researcher primarily responsible.  After all, it is their name on the paper.


  Another way of asking this is whether researchers have a duty to police their own IRB, potentially second-guessing their approvals.


Well, the researcher ought to make sure they think the work is ethically OK before submitting to the IRB in the first place.  But if they start having doubts later, or they are ethically uncomfortable with changes recommended by the IRB, they should not proceed until those issues are resolved.  So in short: yes.