Do violations of basic ethical principles in research invalidate the results of a study?

I'm working on an ethics workshop for MSc-level anthropology students on the topic of 'Ethics in the Research of Contemporary Populations'. The question posted here will appear at the end of the class, and I would love to show the students as many answers as possible from scientists. Additionally, if the responses demonstrate significant interest, I will consider public dissemination on social media, so please reply anonymously.