Question

Do economists have any particular expertise at making normative arguments? In other words, they have expertise at making positive statements (i.e., what will happen) about some economic policy, for example, but

do they have special expertise to judge whether or not

the policy should be undertaken?

Short answer

Yes, Economists are most likely to have expertise in making normative arguments.

Step-by-step solution

Basic Concept 

Positive Statement shows how a situation actually is. It denotes Economic Problems, it is descriptive in nature. It is objective & verifiable. Ex : Actual Growth level in economy is x%.

Normative Statement shows how a situation should be and denote Economic solutions. It is subjective, suggestive & hence not verifiable. Ex: Growth rate in economy should be y%.

Detail Explanation 

Economists are economics specialists, who have properly structured expert knowledge of production, consumption, investment and other economic activities.

These people - based on these expertise, are likely to be considered more reliable regarding normative statements, ie how things ought to be.

Other laymen people are just subjective opinions, not backed by scientific know how base.