I sympathize with the problem, and wish for a solution.<p>That said, its not a symmetrical relationship. One party is pressed into the predicament unwillingly: the refugee or homeless person. Their population can be considered uniform i.e. the presence of a predator is no different than in the general population.<p>The folks offering their home as a refuge, volunteer. Their population <i>may</i> be laced with predators, who could find this relationship to be fertile ground for abuse opportunities. This could increase the risk to the refuge-seeker by one or two orders of magnitude.<p>SO the only ones risking anything above meeting any random new person, is the refugee.<p>This is no fault of all the good people who enter this relationship with open heart and open arms. Its just an unfortunate fact of game theory.