This freedom from prosecution should be consistent with the notion that the individuals involved met as adults and engaged in a consensual romantic relationship without knowing of their genetic heritage. Under such circumstances, no harm is being done, and therefore no punishment is needed. Care should be taken in terms of the way offspring from such relationships are allowed, if it is determined that there is a likelihood of genetic defects due to inbreeding.
As long as the sexual act is consensual between two legal adults or those over the age of consent, then the partners should be free from any legal prosecution. Legal action is meant to protect people from being wronged, but in the case of consensual, adult sexual relations there is no one who is wronged, so there should be no prosecution.
There is really no reason to have a discussion about genetic sexual attraction because sexual attraction is, ultimately, more about social and developmental conventions than a hardwired one. While certain characteristics make people inherently more attractive on average, using these as a justification for anything ignores all that is known about attraction.
I do not think that those who act on genetic sexual attraction should be free from legal prosecution. To suggest otherwise is to think that it is okay for somebody to have sex with small children just because it is in their genes to do so. I think that such an act is a crime and wrong.
No, simply being attracted to someone is not a good excuse for certain sexual behaviors. Things like rape and sexual assault exist because people feel a physical need for intercourse with another person against his or her will. This cannot be excused as a genetic attraction is a serious punishable offense. Excusing inappropriate behavior as genetic is unacceptable.