> we have to add another condition: the net present value of the profits that could be obtained from compromising or sabotaging the network would need to exceed the net present value of the profits that could be obtained in perpetuity from behaving honestly.

I think you have hidden one interesting assumption there. You assume there exists a relatively low upper limit for the interest rate used in npv calculations for all investors. In other words, if there is even one investor at any point of time that needs the money really badly very soon, your argument breaks down.