I just read this. The logic is sound if the only issue was children being born deformed but its not.
Further using your argument does it mean paedophilia should be legal as long as no one gets pregnant?
The incest relationship is not just about making genetically defective children but also creating a plethora of complex negative psychological, emotional and physical health issues other than defective children..
Do you really think someone who has sex with his mother or sister could be healthy and have a positive life?
I have been one on one with incest victims in court. Their stories and the impact on them led me to learn the damage done via incest can be multi-generational, contagious and is very rarely consensual or between people of equal capacity and power.
I am loath to morally judge behaviour but I draw the line with paedophilia, incest, sexual assault and yes I believe laws dealing with sexual behaviour must set limitations.
I do have a Freudian bias as to this issue as well. I follow Freud's conclusions as to the need to limit, i.e. repress certain sexual desires if society is to evolve past basic primate behaviour.
I also believe that while sex has a purpose to procreate life, in the case of humans, it may also have a pleasure function. I don't believe either issue should be used as sole criteria for defining social morale and laws but form part of a wider criteria of considerations.