Some refs are unintentionally biased (read: all), sometimes enough so that it colors their officiating. Some are consciously biased and allow it to color their officiating. All have moments of inattention for whatever reason-- back hurts, thinking of soon-to-be ex-wife that is leaving them, have to sneeze, etc. They are often quick to defer to a colleague, magnifying errors that should have been corrected by a second set of eyes. Often only one set of eyes is on a play, and the moment of inattention means that it is seen out of context or not seen. Multiplying it out, there are on the order of 100,000 instances of a player being on the field for a play in FBS in a week. How curious it would be if millions of detectives with pause and rewind on their screens could find few or no examples of official error in such a large sample.
The problem lies in sorting out and trying to address the distinct forms of error. We are not going to be able to do much for the guy who is distracted because he spends his game trying to hold in a wet fart. The egregious face-mask on the ball-carrier or the all-penalties-on-one-team behavior merits inquiry by a body with the will and ability to apply meaningful consequences.