If somebody actually thinks that a mirror compensates for skills as mentioned earlier, they are simply an idiot but again, we would be talking about the user, not the device. Don't condemn or consider how useful a mirror is based on some moron's inability to know how to use it properly and effectively.
Personally, it's my belief that a person's comfort level with or without a mirror on a bike is directly related to their driving skills. Just my humble opinion. Go ahead, flame me.
I do understand roadies that wear full kit and actually get some speed up out there not wearing mirrors for any reason though. I can excuse that for sure.
side note: with my help we got this sucker to 10 pages! Sorry.