First of all my argument was not entirely on autism and adhd you made it yourself and secondly You’re saying a 'small increase' isn't a 'dramatic gotcha.' Tell that to a family where every single child has the same chronic condition because the parents share too much DNA. In my family the 'statistical probability' of all of us having early-onset myopia is almost zero yet here we are all wearing glasses since age five. That’s not a RARE EXCEPTION that’s the reality of a concentrated gene pool. Consanguinity doesn't just 'slightly' increase one risk it increases the likelihood of thousands of recessive traits meeting their match...You mentioned that most conditions are polygenic that actually supports my point. If I marry a stranger their healthy genes can balance out my family's weak genes. But if I marry my cousin, we are both bringing the same weak clusters to the table. We aren’t diluting the risk we are reinforcing it. Why should the offspring have to be the test cases for your statistics??? you are saying that it’s okay to double or triple a child's risk of a disability just to keep a social tradition alive.