You have a genetic disease which carries a likelihood of being passed on of 1:1000. The symptom of this disease is that the affected person becomes an antinatalist, resenting you for casting them unbidden into the world. There is no pre-natal test and no cure. Do you take the risk? If you do, what probability level would give you pause, 1:100? 1:10? 50/50? If no, is there any level of likelihood that would make you think it was worth it?