"And while royal families in Europe avoided sibling incest, many, including the Hohenzollerns of Prussia, the Bourbons of France, and the British royal family, often married cousins. The Spanish Habsburgs, who ruled for nearly 200 years, frequently married among close relatives. Their dynasty ended in 1700 with the death of Charles II, a king so riddled with health and development problems that he didn't talk until he was four or walk until he was eight. He also had trouble chewing food and couldn't sire a child."
Incest definition: sexual intercourse between persons so closely related that they are forbidden by law to marry.
There are many states in US where marriage between cousins is illegal - hence some reasonable people consider it incest.
Birth defects are doubled with Cousins.
As far as being whores - well, many were, Napoleon was - pretty rampant in the times along with I'm guessing most of mankind throughout the ages... most Marshals had mistresses, though I've never found evidence Davout did.
So I officially apologize for not having invested more time in substantiating the claim, but now I can proudly say that Napoleon was more legitimate than those half-wit bastards of those incestuous whores of European monarchies.