Final answer:
The proposition that Sherrie and Fran have differing views is significant as it stresses the need for an argument to consider various perspectives to ensure its credibility and to strengthen the evidence's relation to the conclusion.
Step-by-step explanation:
The question prompts a discussion on argument validity and the usage of evidence within reasoning. When an argument's premises are inadequate to support its conclusion, it indicates that the argument may lack enough valid points or that the points provided do not logically entail the conclusion. On the other hand, the idea of alternative arguments with equal or greater support suggests that there may be other explanations or viewpoints which are not addressed but have logical strength comparable to or greater than the argument in question. Therefore, in a context where the reasoning is under scrutiny, if Sherrie and Fran are in disagreement and have differing views, this proposition would most significantly justify a discussion on the robustness of an argument by highlighting that not all possible perspectives have been considered and the conclusion might not be as credible as it would be if it took into account a broader range of evidence or argumentation.