A parent accompanying a job interviewee is all the reason I need to reject. I need an employee or co-worker who does not need a parent to get their work done.
While I agree that it is a strong reason to reject, I disagree with the sweeping characterisation as all such interviewees "needing a parent to get their work done". In this very thread, we are reminded that there are people with parents who have mental disorders.
Maybe it's because I tend to assume these situations are usually the parent's issue (not the student's), but I think lightningstrike was just trying to make the point that parents who think they are helping (?) in some way are actually hindering. But yes, mental issues are often a part of the parent's dynamic, so you can't assume a rational argument will have any impact. I had a helicopter parent when I was a student. I, my other family members, and even a few administrators tried to convince them that this behavior was destructive, but my parent believed everyone else was wrong. As macadamia says, you might not think it takes a secret service quality of separation, but I have seen that sometimes it does.