I also think that if they ended the drug war then everyone will start picking up a heroine addiction. //SARCASM//
In regards to the OP, morally I do not agree with that, but I have no business pushing my morals onto anyone except when my wife and I are raising our children.
If they are two consenting parties, then whatever floats your boat.
Now if anyone brings up the genetic risk side of the argument that is out there (i.e. any sort of autosomal recessive disorder, etc.), my response to that then is should the government also dictate whether two unrelated consenting adults can have children if they both carry the same recessive gene mutations (cystic fibrosis, Tay Sachs disease, etc.)? But how will the government get an individual's DNA? ... there are databases out there where people willingly submit their DNA sample, like 23andMe.com, ever since the human genome was mapped. Those sites are for research so to identify specific genes for disease, etc. but we all know about Prism and so just wait until Obama Care really takes off and then procedural costs get linked to what your DNA profile says or maybe in the near future, when you go and apply for a State Marriage licence.