No human being is obligated to conform to someone else’s conception of the Good. Moral rules are expression of the subjective judgments of individuals. As such, they can never acquire objective legitimacy. It follows from this that virtuous indignation and moral outrage can never be objectively justified. They exist, not as rational responses to the breaking of objectively legitimate rules, but as subjective behavioral traits that are usually irritating and occasionally dangerous to others.
Does the above imply that we should not behave morally in our day to day interactions with other human beings? Of course not! There is no other plausible way to regulate those interactions so as to minimize conflict and maximize mutual benefit. We are certainly not intelligent enough to accomplish the same thing in real time using our meager powers of reason. Imagine the tedium of a conversation in which each party had to carefully reason about the potential outcome and impact of every word he spoke. It is to the advantage of all, or at least most of us, that moral rules exist, and that their violation be punished or otherwise prevented. It is, however, reasonable to insist that those rules conform to human nature, be as simple and efficient as possible, and not be motivated by the claims of any religion, whether spiritual or secular.