That's a common misconception, much like many that we as gunowners face. Sure we could pull a gun and kill someone, but we don't. There is the exception like Ft. Hood, but we just don't behave that way. Homeless people tend to be the same way, its a human nature issue really. There are contributing factors to homelessness such as drug and alcohol abuse, or mental illness, but they just don't go around hurting people that are trying to help them. They are typically too busy trying to survive, and maintaining a lower profile, partly to avoid LEO attention, partly due to feeling inadequate or dirty. Most of the time if you help them, they feel towards you like you are above and beyond other people that they might otherwise try to use in one form or another.
ETA, that wasnt pointed at you bud.