First of all, we should note that not all sociologists would feel this way. Some would think that they should use their knowledge to reform society. However, if we must argue that sociologists should simply study dispassionately there are two interconnected arguments that we can put forward.
First, we can argue that dispassionate study leads to better actual research. If a sociologist wishes to reform society, that sociologist is likely to approach his or her work in a biased way. A sociologist who wishes to implement certain reforms is likely to produce research that always argues for that particular reform. This degrades the quality of the sociologist’s work.
Second, we can argue that the sociologist will not be trusted by research subjects or by government decision makers. For example, if a sociologist wanted to end prostitution, the prostitutes they studied might not trust them and might not answer their questions or tolerate their presence. Government officials would also lose trust. They would see the sociologist’s work as advocacy, not as serious scholarship and would be less inclined to act on that work.
For these reasons, we can argue, sociologists should study society objectively and dispassionately rather than trying to reform it.