Can moral certainty be rational?
Yes, if certainty is earned by evidence and context. Moral certainty is irrational when it becomes dogmatism, image management, or refusal to consider relevant facts. But uncertainty is not automatically more rational. Sometimes refusing to judge is just another way of evading what the evidence already shows.
You can be certain that lying to manipulate someone is wrong while still needing context to judge a messy case. You can be certain that your health matters while still revising the training or diet strategy. Certainty is contextual, not omniscient: It means your conclusion is justified by the full evidence currently available, not that no future distinction could ever matter.
Use certainty for fundamentals and careful fact-checking for application. The more concrete and complex the situation, the more deliberately you should check facts, definitions, motives, alternatives, and consequences. Moral seriousness is not the same as moral rigidity: It means staying loyal to reality, not to a frozen first impression.