Society would be better off without the homeless on average, objectively. Why does society have an obligation to assist and protect people who don't contribute

Society would be better off without the homeless on average, objectively. Why does society have an obligation to assist and protect people who don't contribute to society? If you feel some moral imperative to assist some druggie slobbering in his own shit then by all means you do do, but don't rope me into it. The only people with any obligation to assist are their families or those whose religions command them to do so. Neither involve me.