They talk less about mating taboos than formidable cultural divides, like speaking a different language. No one is forcing an American to marry a fellow English speaker, but it is unlikely that he will marry someone who does not speak English. Who does not know how to use a toothbrush. Who'd never heard of George Washington. And so on. In most places on earth you travel 100 miles and customs, languages, widely shared beliefs - everything - changes considerably. Innovation further splits already structured population by erecting new cultural barriers. Not every innovation, I grant you that, but almost any. You say that if it refashions reproductively isolated groups and such refashioning is sufficiently frequent, you have effectively panmictic population. Had that been the case the effective population size would not stay around 10^5 throughout history. You need a mechanism to explain inbreeding; geographical isolation (serial founder effects) accounts only for a fraction of it. Perhaps divisive innovations subdivide the existing structure rather than refashion entirely new divisions.
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