"It might be pointed out that we cannot gain someone's consent to exist; we cannot gain their consent before they exist and by the time they exist it's too late. But the fact that we cannot gain their consent does not mean that we are free to do without it. Suppose you wish to torture someone against their will, you cannot seek your victim's consent – the torture would not then be against their will. It would be absurd to argue that for this reason we are permitted to torture people against their will. Similarly, the fact that prospective parents cannot get the consent of those they plan to bring into existence doesn't magically mean it's OK. Quite the opposite – if you can't get the consent of the person you're going to significantly affect by your action, then the default position is that you don't do whatever it is that's going to affect them. There are exceptions. Pushing someone out of the way of a falling piano is morally right even if no prior consent can be given (if, for instance, there isn't time). But in this kind of case you are preventing someone from coming to great harm. To procreate – to subject someone to a life – does not prevent them coming to harm. Not being created cannot harm them because they don't exist."