This module provides a good guide on how to conduct an interview. First, by listing several sensitive or unlawful issues that you should avoid, and then going into what should be the heart of your interview. Focusing on experience, education, and personality traits that make a candidate a good fit for the job.
A manager might argue that some of these concerns directly relate to a person's ability to perform, but they rarely do. Rather, they are merely prejudices that do not prove a person would be unfit. A manager conducting interviews in an unethical manner could also be setting a precedent on how the business and other employees perform.
The impact and ramifications could be consequential.
Thoughts?