But excluding the procreation aspect, if the people were not raised with that taboo, they would not be mentally harmed by their sexual activities. The study cited is very poor science as it has no control group. In order to test a taboo, one would have to subjects of both perspectives..
Can you cite a scientific study to support your claim?
do you have a scientific study to support the harm argument?
I think "mental harm" is like god... burden of proof is on the harm side.