There are legitimate concerns that preprint servers may become venues for posting and providing some validation for “pseudoscience,” low-quality research results, or even papers that pose serious ethical or national security concerns.
Many preprint servers screen papers before posting. arXiv has faced these issues with climate science and has largely managed to block or mitigate issues surrounding attempts to propagate misinformation.
Since the potential public impact of papers relevant to public health increases the dangers of posting misleading information, the medical preprint server medRxiv carries out more stringent screening than bioRxiv. While there are dangers inherent in distributing medically-relevant information prior to peer review, the server has also been influential in increasing early feedback and visibility of important COVID-19 research and thus played a major role in pandemic response. See ASAPbio’s resource on preprints in COVID-19.
Furthermore, some preprint servers display disclaimers on the top of each article to make clear that preprints have not been certified by peer review. In fact, it can be much more damaging when misinformation is conveyed through a journal, which carries an implicit stamp of approval from the scientific community (a case in point being the connection of vaccines to autism which was published in a major medical journal).
Many preprint servers also have policies about when content can be completely removed for ethical or legal reasons. The leak of personal data from the dating website OKCupid under a scientific pretense provides an example of behavior in this category.
For more information about screening, withdrawal/removal, and disclaimers, see the Preprint Server Directory.