Conditional Obligation and Detachment

Suppose that John has a moral obligation to stop smoking given that smoking is dangerous to his health. Suppose further that smoking is dangerous to his health. Does it follow that John has a moral obligation to stop smoking? Although intuition inclines one to answer in the affirmative, recent developments in deontic logic apparently call this inference into question. The issue at hand is whether unconditional obligations are detachable from conditional obligations on the basis of purely factual considerations. I believe that they are not. In the course of arguing for this position I defend a novel restricted rule of detachment which is constructed out of both factual and normative components.