Obviously it is our empirical sensory tools, but that's only half of the point, let me rephrase my main objection here using your own sentence:
"Using the ability to identify categories based on optical differences in order to generalized people based on observable physical pattern"
Take for instance the observation that you have a blue eyes is not the problem, but it is to classify you inside "the blue eyes people" category, then to further build up some collective personality based on that variable, for instance what is the average income of "the blue eyes" in comparison with "the green eyes"? How prone "the blue eyes" to commit crimes in comparison to "the green eyes"? These information not without impact, it will be used to crafted the collective personality for instance "the blue eyes are mostly less successful and more prone to crime in comparison to the green eyes". This thinking shortcut might have its function to save our budd back then, but it's only serves as a mean prejudice now. Berzerker put a very good and honest wording for this:
It is not the fact of its primordial traits of human that makes it dreadful, but how it corrupts the society with the false negative alarm that makes it bad. It's your old spyware system that delivered you a tons of false negative, resulting you to deletes so many important data in your computer.
I can recognized your unique physical attribute without lumping you in a box of collective physical category that I precept to be your group, then subconsciously or consciously start to related you with certain subset group personality that already crafted within that category.