… I have been wondering about issues of taboos in porn. Perhaps the most significant example is that themes of incest have become very popular, it seems. What little I've been able to ask people about it, the interest seems to be that the con…
I don't know if I have enough information to offer a response to your thoughtful question.
First, if sex is the result of coercion, it is always wrong, and incest is often coercive.
Your question leads into a discussion of "the age of consent." States establish those laws based on an arbitrary assignment of a number. The laws often don't reflect what is actually happening. Many adolescents who are under-age by the law's definition are having sex (although this has diminished somewhat in recent years.)
But laws cannot be made based on a level of maturity. Some adolescents may be capable of making responsible decisions; others are not. Some are damaged by this; others are not. But a lot of adolescents who are not strictly legal are having sex.
Another issue, that I have addressed in my writing, are the Daddy/son, Uncle/nephew role plays. Initially I struggled with this because of the implications that they were incestuous.
However, I now see this more as fetishistic (not a necessary thing but used to enhance the sexual experience.) I also see them in more of a metaphorical sense than a literal one.
For example, a young man is attracted to the characteristics frequently attributed to "daddies," (maturity, experience, safety, etc.) and not attracted to the fact there is some biologic relationship.
Here is something I wrote about it: https://medium.com/an-idea/age-as-a-factor-in-sexual-orientation-and-attraction-8a8954e87bf6