This study explores why nongovernmental organizations (NGOs) engage in unethical behavior because of, and not despite, their perceived moral integrity. Contrary to expectations, we show how a glorified perception of moral integrity within NGOs can create blind spots for unethical behavior, a phenomenon termed the NGO halo effect. The NGO halo consists of people in NGOs glorifying the moral goodness of their organization's mission, morals, and people and prioritizing them over other considerations, the effect of which is unethical behavior. The relationship between the NGO halo and NGO unethical behavior has not been measured. We conduct two studies to measure the relationship between the NGO halo and NGO unethical behavior. In Study 1 (N = 256), we define and establish the content validity of the two NGO halo effect constructs. In Study 2 (N = 544), we validate the constructs and use a regression design to show that the NGO halo is positively and significantly related to unethical behavior. Our research reveals the dark side of moral idealization and confirms that the NGO halo effect is a risk factor for NGO unethical behavior.