It makes sense to live in the here and now not base laws on theoretical future societies.
For now, there is no place for incest in modern societies and I can't see any reason why it should be legalised.
Can you?
Yes.
It punishes people for doing something that damages no one in an arbitrarial way.
I am not saying we should base our laws in theoretial future societies. I am saying we shouldn´t turn off our brain and not argue against laws that are unfair to others.
If it wasn´t for people that were ahead of the here and now for their times, the here and now of today would be full of black slavery, witch burnings, women treated as not even citizens, etc.
You need to see beyond what you have in front of you.
Yes, I will always defend living in the here and now, but also I must defend understanding waht we NEED here and now.
I don´t like incestuous relationship as a principle, but I understand that condemning them just because I dn´t like them is the same as condemning black people because people felt they were inferior, condemning women because men would feel treathened with them having more power, etc.
now if you think none of this things have nothing to do with it, you might need to get a little abstract logic practice. Patterns exist in human behaviour, wether you want/can look at them, or not.