I understand where you're coming from, but there are problems with this kind of argument. Think of things which are, or have been, frowned upon, e.g. interracial marriages or marriages across 'classes', single parents and, as a contemporary example, homosexual parents. Similarly, is it selfish for parents to follow eccentric pursuits (e.g. wearing extravagent outfits or dancing to music on the front porch) if their children might be teased/persecuted for it? My feeling is that we have it the wrong way round when we try to make people give up behaviors which aren't fully socially condoned instead of challenging the intolerant position of social conservatives. Of course, incest is more difficult because most cases, I would guess, fall into the dubious/pathological category that we want to try and prohibit. It may be unreasonable to expect people to learn to differentiate between 'acceptable' and 'unacceptable' incest, but so goes my standard utopian pipe dream of tolerance.
