There are two main issues with incest: 1) offspring, which should be avoided unless you check the embryos for issues and discard any that would have health problems due to inbreeding, and 2) the possible existence of power dynamics that might make consent too questionable to be acceptable.
Two sufficiently mature (I think this excludes about 90% of the population, but that’s probably my cynicism talking) adults, who have the means to live independently (so no dangerous power dynamics), and at least one of which is naturally or artificially sterile (or who physically can’t have children for other reasons, for instance due to having incompatible genitals), sure, go ahead, have fun.
Otherwise, there’s too much risk of harming one or both of the participants, or their potential offspring.
There are two main issues with incest: 1) offspring, which should be avoided unless you check the embryos for issues and discard any that would have health problems due to inbreeding, and 2) the possible existence of power dynamics that might make consent too questionable to be acceptable.
Two sufficiently mature (I think this excludes about 90% of the population, but that’s probably my cynicism talking) adults, who have the means to live independently (so no dangerous power dynamics), and at least one of which is naturally or artificially sterile (or who physically can’t have children for other reasons, for instance due to having incompatible genitals), sure, go ahead, have fun.
Otherwise, there’s too much risk of harming one or both of the participants, or their potential offspring.