The value of people

Upon what do we base our valuation of people?  This is something we all do, either consciously or subconsciously.  This is something learned and if not addressed and thought through, it becomes something we do without consideration of truth or falsity. 
Do we, upon seeing a homeless person, a drug addict, a prostitute, a transvestite, or a gang member, immediately think less of that person?  Do we hold some sort of racist tendencies, sometimes without thinking?
Social experiments have been done with "homeless" people and "business executives".  It's sad to see how people actually respond when they don't know they are being watched.
Do we judge others who are trapped in a particular sin that we personally find repulsive, but "wink" at other sins?  Do we explain away our own sins while strongly criticizing others for their sins?
And even more importantly, do we devalue some people because of their particular sins?
Give it some thought.