The focus of the article is epistemological problems arising in the field of ethical regulation of biomedical researches and technologies. The bioethical expertise seeks to limit or to prohibit certain directions of research into biomedical reality, assessing the possible negative consequences of their application in human society. However, in this case, subject to expert evaluation is not biomedical research or technology itself, but rather the moral potential of individual actors of scientific production and society in general, i. e. bioethics (we note, not without reason) does not trust man and society, and therefore declares the extreme importance of ethical regulation in this and adjacent areas. At the same time, the actual cognitive component of such a research remains outside of expertise, blocked by bioethics itself, which leads to an increasing value of socio-cultural (regional and pragmatic) relativity of ethical assessments of the admissibility of biomedical developments. We believe that the epistemological potential of the thought experiment, which allows us to build a model for the realization of the real impracticable (and specifically in bioethics, the morally uncertain), allows us to expand the cognitive component of expert evaluations. Thus, the thought experiment opens an additional opportunity to clarify (concretize) the real sphere of applicability of the principles and norms of bioethics through the interaction of social, humanitarian and natural sciences in expert assessments.