Evidence of harm can be shown through scientific means other than randomized trials – particularly in cases where engaging in such experimental research would increase the risk for suicidality. For example, in the case of sexual orientation conversion therapy the evidence of harm has been shown in a systematic review (Przeworski, Peterson & Alexandra, 2020) and observational studies have documented increased suicide risk among sexual minority youth who were forced to participate in sexual orientation conversion efforts (see Ryan et al, 2020). Randomly assigning sexual minority youth to experience SOCE would violate minimum acceptable standards for risk to subjects in research studies, and would violate the research ethics for all disciplines.
Sources:
Przeworski, A., Peterson, E., & Piedra, A. (2020). A systematic review of the efficacy, harmful effects, and ethical issues related to sexual orientation change efforts. Clinical Psychology: Science and Practice, n/a, e12377. https://doi.org/10.1111/cpsp.12377
Ryan, C., Toomey, R. B., Diaz, R. M., & Russell, S. T. (2020). Parent-Initiated Sexual Orientation Change Efforts With LGBT Adolescents: Implications for Young Adult Mental Health and Adjustment. Journal of Homosexuality, 67(2), 159–173. https://doi.org/10.1080/00918369.2018.1538407