That, and I think a lot of it is also pattern matching. When we hear that someone is homeless, we compare that person to the mental image we have of the homeles

That, and I think a lot of it is also pattern matching. When we hear that someone is homeless, we compare that person to the mental image we have of the homeless people we've encountered on the streets. One of the great tragedies of our society is that we've allowed our mentally ill to slip through the cracks. Untreated schizophrenics and PTSD-suffering Vietnam veterans may or may not make up a significant percentage of the homeless we see -- but they're certainly the most memorable. They stand out. They ingrain, in passersby, a mental map of homeless people as "crazy," or "violent," or "dangerous." And so we start to believe that homeless people are broken somehow. Many people go a step further; they start to regard the homeless as less than human. These pattern matches are powerful blocks on empathy for many, many people.