There are too many things that we take for granted. The picture says 'if you would not make her a wife don't make her a mother.' In an imperfect world, if you make her a mother but still cannot make her a wife, treat her like a wife and be a father to your children.
My fear of unprotected sex has little to do with catching illnesses. My biggest concern is the possibility of being the father of children without knowning that I am their father and of being unable to look after them. For me the expression 'blood is thicker than water' is linked to physical and emotional pain.