I, having experienced fraud in the context of monogamy, as well as many other mechanisms as well, heartily approve of your broaching this subject.

Fraud, whether for financial gain, or to obtain other benefits, generates those benefits absent the agreed upon compensation for those benefits. Since the money in a financial transaction can be equated to hours of labor, extracting that money without providing the agreed upon compensation is equivalent to enslaving the defrauded party. Fraud in a marriage achieves the same enslavement, only the labor isn't first translated into money, for the most part, but rather remains in it's original form, such as fealty, devotion, mutual division of marital burdens, etc..

Frankly, I see marital fraud as far worse than financial fraud, as personally I care more about people than money. I am not alone in that perception, as there are far more adverse impacts on people due to marital fraud than financial, and this can be measured. The numbers of people who suffer suicidal ideation and lesser emotional and mental trauma is vastly greater due to marital fraud than financial.

If this logical extension of fraud to enslavement isn't accepted by voluntarists, then clearly there are simply other things besides aggression that violate individual sovereignty, and fraud then is one of those things.

Is theft aggression? Fraud is just a form of theft that depends on duplicity. How about lying? Unless these things are labeled aggression, the voluntarist concept is far short of complete.