[Koko Ed]

This comes up every year (and it will come up again and again) and to be honest it doesn't matter what we say, People will see what they want to see and if they believe that teams that have mentors who build their robots (or even assist in any way shape or form) are the root of evil.
Perhaps the only way to deal with it is to let them stew in their own juices and take them off your pick list. Sometimes the best lessons come with a swift kick to the rear.