I don't know they trivialise it so much as overlook it.
Everyone gets quite caught up in the "EWWW MUTANT KIDS" thing, but that's not really how genetics works - it would typically take more than one incestuous generations to start making genetic issues likely and pronounced, so it's unlikely to be the reason for prohibiting incest.
It's also an argument for why many places don't consider cousin-cousin to be incest (i.e. cousin-cousin isn't prohibited, only siblings and direct ancestors/descendants, NSW being one of them last I checked) - they're not AS genetically overlapping, but it's still there. (In fact, there was a population study in Denmark or some other small-population European country which suggested that it's good for the gene pool to have a certain amount of cousin or second cousin breeding).