Public outcry for radical isolation and quarantine policies followed the first Ebola diagnosis in the United States when Eric Duncan, upon his return home Oct 2014 from West Africa, then in the midst of a catastrophic Ebola epidemic, tested positive for Ebola. Likewise, the Dec 2014 Disneyland measles outbreak unleashed an angry backlash against parents who refused to have their children vaccinated; and there was public momentum to repeal all legal exemptions to mandatory vaccination of school children. This paper presents an ethical and legal analysis to adjudicate the issue which is at stake in both controversies; namely the inherent conflict between individual rights v. public health when the nation is threatened by serious communicable disease. It presents reasoned arguments, weighing duty-based v. consequence-maximizing ethical principles of right action through application of the felicity calculus (net utility). And the paper demonstrates how the metaethical theory of emotivism is operative in formation and expression of public sentiment which fueled the ethical and legal deliberations.