If it were true that there are no moral principles then I'm not sure how society would function. It seems to me that we need moral rules in order to help us to learn how to behave and to attribute praise or blame on others' behaviour. Moral principles function in the realm of moral behaviour in the same way that rules of the road function for drivers. Would Dancy argue that there are no rules of the road, and in every instance the choices are context specific?
Attempting another analogy, could it be the case that our moral code is a bit like a recipe - if we follow the recipe then we end up with the outcome that we seek. In the case of cooking, we end up with a meal. In the case of normative behaviour, we end up with a functioning society.
No recipe should ever be followed in every circumstance, we have to allow for many factors such as the preferences of the guests, the temperature of the oven, the nature of the ingredients. The fact that we have to use judgement in the way we follow the recipe clearly can't lead us to conclude that the recipe doesn't exist.