We would simply ask users to evaluate: "If we assume the argument to be true, would it strengthen the conclusion?" This way "the grass is green" can still have a high score, but it won't contribute any points to the belief that "we should have an estate tax", because we would multiply the argument score (assumed to be positive for the belief that grass is green) by the linkage score (assumed to be 0% or single digits) between the two.
Lazy users should be allowed to just up or down-vote a linkage between an argument and its conclusion. However, people could also post reasons to support or oppose a linkage. People could up or down-vote these arguments, which would also affect the linkage score. People could post all all categories of reasons to support or oppose a linkage. For example, they could post scientific studies that support the linkage between high sugar diets and diabetes.