two lesbian twin sisters who are both 25 years old who are in an incestuous relationship with each other is morally okay in my opinion because what they’re doing is completely harmless.
Just because society thinks it’s gross and weird that doesn’t mean that it’s morally wrong.
Cum causes cancer. Do you know of anyone with cancer that wasn’t born via some method involving cum? Exactly.
Artificial insemination, despite the name, doesn’t require sperm; just DNA. There are loads (pun intended) of people born without having come from cum.