A similar question, in terms of the content of the social implications course, would be how effective would the course be if it did not count for any marks. Many instructors have experience teaching either a required and unpopular course, or a course that has required and unpopular material. For instance in an introductory data structures course there is a requirement that students be taught some analysis of algorithms. This material, and the mathematics associated with it, is not popular with many students, and as a result many instructors will marginalize the material.
Instructors, in an attempt to reassure the students, will make statements like "don't worry, if you don't understand induction you could still get an A on the final exam" or "once this course is over you will never see this stuff again". It is not the instructor's intent to have students decide that the respective material is unnecessary, but often that is the consequence.
Many students in computing or engineering are drawn to their respective disciplines because of their apparent objectivity. This apparent objectivity is missing in the study of the social implications of technology. Because of this perceived lack of objectivity, students often feel uneasy about the material and, as with other unpopular material, would like to avoid it. Avoidance is far more viable if, as with the analysis of algorithms part of an introductory data structures course, the material makes up a small part of a larger course. With the current ACM requirement of about 10 hours, it is possible to cover the required content and, if it counts for an appropriate share of the final grade, the student could still get a B in the course and not understand any of the material on the social implications of technology. Of course if the material is divided up and taught as part of a number of courses, then it could have no impact at all on the grades of the students.
If the material on the social implications of technology has no impact on the grades of the students, then it is far less likely to have an impact on the students themselves. As a result, it is necessary to have at least a single course where the entire grade is based on the understanding of the social implications of technology.