Both.

VNM doesn't offer any "formulation of rational behavior". VNM says that a function with a particular set of properties must exist and relies on assumptions that do not necessarily hold in real life.

I also don't think that a utility function that can condense the risk preferences into a single scalar is likely to be accurate enough for practical purposes.

You are looking at the wrong meta level.

When I say "VNM doesn't offer any formulation of rational behavior" I'm not disagreeing with any particular axiom. It's like I'm saying that an orange is not an apple and you respond by asking me what kind of apples I dislike.

*0 points [-]Which (possibly all) of the VNM axioms do you think are not appropriate as part of a formulation of rational behavior?

I think the Peano natural numbers is a reasonable model for the number of steins I own (with the possible exception that if my steins fill up the universe a successor number of steins might not exist). But I don't think the Peano axioms are a good model for how much beer I drink. It is not the case that all quantities of beer can be expressed as successors to 0 beer, so beer does not follow the axiom of induction.

I think ZFC axioms are a poor model of impressionist paintings. For example, it is not the case that for every impressionist paintings

xandy, there exists an impressionist painting that contains bothxandy. Therefore impressionist paintings violate the axiom of pairing.